Intraoral 3d scanner employing multiple miniature cameras and multiple miniature pattern projectors

ABSTRACT

An apparatus for intraoral scanning includes an elongate handheld wand that has a probe. One or more light projectors and two or more cameras are disposed within the probe. The light projectors each has a pattern generating optical element, which may use diffraction or refraction to form a light pattern. Each camera may be configured to focus between 1 mm and 30 mm from a lens that is farthest from the camera sensor. Other applications are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from:

-   -   (a) U.S. Provisional Application No. 62/689,006 to Saphier,        filed Jun. 22, 2018, entitled, “Intraoral 3D scanner employing        multiple miniature cameras and multiple miniature pattern        projectors,”    -   (b) U.S. Provisional Application No. 62/775,787 to Atiya, filed        Dec. 5, 2018, entitled, “Light field intraoral 3D scanner with        structured light illumination,” and    -   (c) U.S. Provisional Application No. 62/778,192 to Atiya, filed        Dec. 11, 2018, entitled, “Light field intraoral 3D scanner with        structured light illumination.”

Each of these applications is assigned to the assignee of the presentapplication and is incorporated herein by reference in its entirety forall purposes.

FIELD OF THE INVENTION

The present invention relates generally to three-dimensional imaging,and more particularly to intraoral three-dimensional imaging usingstructured light illumination.

BACKGROUND

Dental impressions of a subject's intraoral three-dimensional surface,e.g., teeth and gingiva, are used for planning dental procedures.Traditional dental impressions are made using a dental impression trayfilled with an impression material, e.g., PVS or alginate, into whichthe subject bites. The impression material then solidifies into anegative imprint of the teeth and gingiva, from which athree-dimensional model of the teeth and gingiva can be formed.

Digital dental impressions utilize intraoral scanning to generatethree-dimensional digital models of an intraoral three-dimensionalsurface of a subject. Digital intraoral scanners often use structuredlight three-dimensional imaging. The surface of a subject's teeth may behighly reflective and somewhat translucent, which may reduce thecontrast in the structured light pattern reflecting off the teeth.Therefore, in order to improve the capture of an intraoral scan, whenusing a digital intraoral scanner that utilizes structured lightthree-dimensional imaging, a subject's teeth are frequently coated withan opaque powder prior to scanning in order to facilitate a usable levelof contrast of the structured light pattern, e.g., in order to turn thesurface into a scattering surface. While intraoral scanners utilizingstructured light three-dimensional imaging have made some progress,additional advantages may be had.

SUMMARY OF THE INVENTION

The use of structured light three-dimensional imaging may lead to a“correspondence problem,” where a correspondence between points in thestructured light pattern and points seen by a camera viewing the patternneeds to be determined. One technique to address this issue is based onprojecting a “coded” light pattern and imaging the illuminated scenefrom one or more points of view. Encoding the emitted light patternmakes portions of the light pattern unique and distinguishable whencaptured by a camera system. Since the pattern is coded, correspondencesbetween image points and points of the projected pattern may be moreeasily found. The decoded points can be triangulated and 3D informationrecovered.

Applications of the present invention include systems and methodsrelated to a three-dimensional intraoral scanning device that includesone or more cameras, and one or more pattern projectors. For example,certain applications of the present invention may be related to anintraoral scanning device having a plurality of cameras and a pluralityof pattern projectors.

Further applications of the present invention include methods andsystems for decoding a structured light pattern.

Still further applications of the present invention may be related tosystems and methods of three-dimensional intraoral scanning utilizingnon-coded structured light patterns. The non-coded structured lightpatterns may include uniform patterns of spots, for example.

For example, in some particular applications of the present invention,an apparatus is provided for intraoral scanning, the apparatus includingan elongate handheld wand with a probe at the distal end. During a scan,the probe may be configured to enter the intraoral cavity of a subject.One or more light projectors (e.g., miniature structured lightprojectors) as well as one or more cameras (e.g., miniature cameras) arecoupled to a rigid structure disposed within a distal end of the probe.Each of the structured light projectors transmits light using a lightsource, such as a laser diode. Each light projector may be configured toproject a pattern of light defined by a plurality of projector rays whenthe light source is activated. Each camera may be configured capture aplurality of images that depict at least a portion of the projectedpattern of light on an intraoral surface. In some applications, thestructured light projectors may have a field of illumination of at least45 degrees. Optionally, the field of illumination may be less than 120degrees. Each of the structured light projectors may further include apattern generating optical element. The pattern generating opticalelement may utilize diffraction and/or refraction to generate a lightpattern. In some applications, the light pattern may be a distributionof discrete unconnected spots of light. Optionally, the light patternmaintains the distribution of discrete unconnected spots at all planeslocated between 1 mm and 30 mm from the pattern generating opticalelement, when the light source (e.g., laser diode) is activated totransmit light through the pattern generating optical element. In someapplications, the pattern generating optical element of each structuredlight projector may have a light throughput efficiency, i.e., thefraction of light falling on the pattern generator that goes into thepattern, of at least 80%, e.g., at least 90%. Each of the camerasincludes a camera sensor and objective optics including one or morelenses.

A laser diode light source and diffractive and/or refractive patterngenerating optical elements may provide certain advantages in someapplications. For example, the use of laser diodes and diffractiveand/or refractive pattern generating optical elements may help maintainan energy efficient structured light projector so as to prevent theprobe from heating up during use. Further, such components may helpreduce costs by not necessitating active cooling within the probe. Forexample, present-day laser diodes may use less than 0.6 Watts of powerwhile continuously transmitting at a high brightness (in contrast, forexample, to a present-day light emitting diode (LED)). When pulsed inaccordance with some applications of the present invention, thesepresent-day laser diodes may use even less power, e.g., when pulsed witha duty cycle of 10%, the laser diodes may use less than 0.06 Watts (butfor some applications the laser diodes may use at least 0.2 Watts whilecontinuously transmitting at high brightness, and when pulsed may useeven less power, e.g., when pulsed with a duty cycle of 10%, the laserdiodes may use at least 0.02 Watts). Further, a diffractive and/orrefractive pattern generating optical element may be configured toutilize most, if not all, the transmitted light (in contrast, forexample, to a mask which stops some of the rays from hitting theobject).

In particular, the diffraction- and/or refraction-based patterngenerating optical element generates the pattern by diffraction,refraction, or interference of light, or any combination of the above,rather than by modulation of the light as done by a transparency or atransmission mask. In some applications, this may be advantageous as thelight throughput efficiency (the fraction of light that goes into thepattern out of the light that falls on the pattern generator) is nearly100%, e.g., at least 80%, e.g., at least 90%, regardless of the pattern“area-based duty cycle.” In contrast, the light throughput efficiency ofa transparency mask or transmission mask pattern generating opticalelement is directly related to the “area-based duty cycle.” For example,for a desired “area-based duty cycle” of 100:1, the throughputefficiency of a mask-based pattern generator would be 1% whereas theefficiency of the diffraction- and/or refraction-based patterngenerating optical element remains nearly 100%. Moreover, the lightcollection efficiency of a laser is at least 10 times higher than an LEDhaving the same total light output, due to a laser having an inherentlysmaller emitting area and divergence angle, resulting in a brighteroutput illumination per unit area. The high efficiency of the laser anddiffractive and/or refractive pattern generator may help enable athermally efficient configuration that limits the probe from heating upsignificantly during use, thus reducing cost by potentially eliminatingor limiting the need for active cooling within the probe. While, laserdiodes and DOEs may be particularly preferable in some applications,they are by no way essential individually or in combination. Other lightsources, including LEDs, and pattern generating elements, includingtransparency and transmission masks, may be used in other applications.

In some applications, in order to improve image capture of an intraoralscene under structured light illumination, without using contrastenhancement means such as coating the teeth with an opaque powder, theinventors have realized that a distribution of discrete unconnectedspots of light (as opposed to lines, for example) may provide animproved balance between increasing pattern contrast while maintaining auseful amount of information. In some applications, the unconnectedspots of light have a uniform (e.g., unchanging) pattern. Generallyspeaking, a denser structured light pattern may provide more sampling ofthe surface, higher resolution, and enable better stitching of therespective surfaces obtained from multiple image frames. However, toodense a structured light pattern may lead to a more complexcorrespondence problem due to there being a larger number of spots forwhich to solve the correspondence problem. Additionally, a denserstructured light pattern may have lower pattern contrast resulting frommore light in the system, which may be caused by a combination of (a)stray light that reflects off the somewhat glossy surface of the teethand may be picked up by the cameras, and (b) percolation, i.e., some ofthe light entering the teeth, reflecting along multiple paths within theteeth, and then leaving the teeth in many different directions. Asdescribed further hereinbelow, methods and systems are provided forsolving the correspondence problem presented by the distribution ofdiscrete unconnected spots of light. In some applications, the discreteunconnected spots of light from each projector may be non-coded.

In some applications, the field of view of each of the cameras may be atleast 45 degrees, e.g., at least 80 degrees, e.g., 85 degrees.Optionally, the field of view of each of the cameras may be less than120 degrees, e.g., less than 90 degrees. For some applications, one ormore of the cameras has a fisheye lens, or other optics that provide upto 180 degrees of viewing.

In any case, the field of view of the various cameras may be identicalor non-identical. Similarly, the focal length of the various cameras maybe identical or non-identical. The term “field of view” of each of thecameras, as used herein, refers to the diagonal field of view of each ofthe cameras. Further, each camera may be configured to focus at anobject focal plane that is located between 1 mm and 30 mm, e.g., atleast 5 mm and/or less than 11 mm, e.g., 9 mm-10 mm, from the lens thatis farthest from the respective camera sensor. Similarly, in someapplications, the field of illumination of each of the structured lightprojectors may be at least 45 degrees and optionally less than 120degrees. The inventors have realized that a large field of view achievedby combining the respective fields of view of all the cameras mayimprove accuracy due to reduced amount of image stitching errors,especially in edentulous regions, where the gum surface is smooth andthere may be fewer clear high resolution 3-D features. Having a largerfield of view enables large smooth features, such as the overall curveof the tooth, to appear in each image frame, which improves the accuracyof stitching respective surfaces obtained from multiple such imageframes. In some applications, the total combined field of view of thevarious cameras (e.g., of the intraoral scanner) is between about 20 mmand about 50 mm along the longitudinal axis of the elongate handheldwand, and about 20-40 mm in the z-axis, where the z-axis may correspondto depth. In further applications, the field of view may be at least 20mm, at least 25 mm, at least 30 mm, at least 35 mm, or at least 40 mmalong the longitudinal axis. In some embodiments, the combined field ofview may change with depth (e.g., with scanning distance). For example,at a scanning distance of about 4 mm the field of view may be about 40mm along the longitudinal axis, and at a scanning distance of about 14mm the field of view may be about 45 mm along the longitudinal axis. Ifmost of the motion of the intraoral scanner is done relative to the longaxis (e.g., longitudinal axis) of the scanner, then overlap betweenscans can be substantial. In some applications, the field of view of thecombined cameras is not continuous. For example, the intraoral scannermay have a first field of view separated from a second field of view bya fixed separation. The fixed separation may be, for example, along thelongitudinal axis of the elongate handheld wand.

In some applications, a method is provided for generating a digitalthree-dimensional image of an intraoral surface. It is noted that a“three-dimensional image,” as the phrase is used in the presentapplication, is based on a three-dimensional model, e.g., a point cloud,from which an image of the three-dimensional intraoral surface isconstructed. The resultant image, while generally displayed on atwo-dimensional screen, contains data relating to the three-dimensionalstructure of the scanned object, and thus may typically be manipulatedso as to show the scanned object from different views and perspectives.Additionally, a physical three-dimensional model of the scanned objectmay be made using the data from the three-dimensional image.

For example, one or more structured light projectors may be driven toproject a distribution of discrete unconnected spots of light on anintraoral surface, and one or more cameras may be driven to capture animage of the projection. The image captured by each camera may includeat least one of the spots.

Each camera includes a camera sensor that has an array of pixels, foreach of which there exists a corresponding ray in 3-D space originatingfrom the pixel whose direction is towards an object being imaged; eachpoint along a particular one of these rays, when imaged on the sensor,will fall on its corresponding respective pixel on the sensor. As usedthroughout this application, including in the claims, the term used forthis is a “camera ray.” Similarly, for each projected spot from eachprojector there exists a corresponding projector ray. Each projector raycorresponds to a respective path of pixels on at least one of the camerasensors, i.e., if a camera sees a spot projected by a specific projectorray, that spot will necessarily be detected by a pixel on the specificpath of pixels that corresponds to that specific projector ray. Valuesfor (a) the camera ray corresponding to each pixel on the camera sensorof each of the cameras, and (b) the projector ray corresponding to eachof the projected spots of light from each of the projectors, may bestored during a calibration process, as described hereinbelow.

Based on the stored calibration values a processor may be used to run acorrespondence algorithm in order to identify a three-dimensionallocation for each projected spot on the surface. For a given projectorray, the processor “looks” at the corresponding camera sensor path onone of the cameras. Each detected spot along that camera sensor pathwill have a camera ray that intersects the given projector ray. Thatintersection defines a three-dimensional point in space. The processorthen searches among the camera sensor paths that correspond to thatgiven projector ray on the other cameras and identifies how many othercameras, on their respective camera sensor paths corresponding to thegiven projector ray, also detected a spot whose camera ray intersectswith that three-dimensional point in space. As used herein throughoutthe present application, if two or more cameras detect spots whoserespective camera rays intersect a given projector ray at the samethree-dimensional point in space, the cameras are considered to “agree”on the spot being located at that three-dimensional point. Accordingly,the processor may identify three-dimensional locations of the projectedpattern of light based on agreements of the two or more cameras on therebeing the projected pattern of light by projector rays at certainintersections. The process is repeated for the additional spots along acamera sensor path, and the spot for which the highest number of cameras“agree” is identified as the spot that is being projected onto thesurface from the given projector ray. A three-dimensional position onthe surface is thus computed for that spot.

Once a position on the surface is determined for a specific spot, theprojector ray that projected that spot, as well as all camera rayscorresponding to that spot, may be removed from consideration and thecorrespondence algorithm may be run again for a next projector ray.Ultimately, the identified three-dimensional locations may be used togenerate a digital three-dimensional model of the intraoral surface.

In a further example, a method of generating a digital three-dimensionalmodel of an intraoral surface may include projecting a pattern ofdiscrete unconnected spots onto an intraoral surface of a patient usingone or more light projectors disposed in a probe at a distal end of anintraoral scanner, wherein the pattern of discrete unconnected spots isnon-coded. The method may further include capturing a plurality ofimages of the projected pattern of unconnected spots using two or morecameras disposed in the probe, decoding the plurality of images of theprojected pattern in order to determine three-dimensional surfaceinformation of the intraoral surface, and using the three-dimensionalsurface information to generate a digital three-dimensional model of theintraoral surface. Decoding the plurality of images may includeaccessing calibration data that associates camera rays corresponding topixels on a camera sensor of each of the two or more cameras to aplurality of projector rays, wherein each of the plurality of projectorrays is associated with one of the discrete unconnected spots. Thedecoding may further include determining intersections of projector raysand camera rays corresponding to the projected pattern of discreteunconnected spots using the calibration data, wherein intersections ofthe projector rays and the camera rays are associated withthree-dimensional points in space. The decoding may further includeidentifying three-dimensional locations of the projected pattern ofdiscrete unconnected spots based on agreements of the two or morecameras on there being the projected pattern of discrete unconnectedspots by projector rays at certain intersections.

There is therefore provided, in accordance with some applications of thepresent invention, apparatus for intraoral scanning, the apparatusincluding:

an elongate handheld wand including a probe at a distal end of thehandheld wand;

a rigid structure disposed within a distal end of the probe;

one or more structured light projectors coupled to the rigid structure;and

one or more cameras coupled to the rigid structure.

In some applications, each structured light projector may have a fieldof illumination of 45-120 degrees. Optionally, the one or morestructured light projectors may utilize a laser diode light source.Further, the structure light projector(s) may include a beam shapingoptical element. Further still, the structured light projector(s) mayinclude a pattern generating optical element.

The pattern generating optical element may be configured to generate adistribution of discrete unconnected spots of light. The distribution ofdiscrete unconnected spots of light may be generated at all planeslocated between 1 mm and 30 mm from the pattern generating opticalelement when the light source (e.g., laser diode) is activated totransmit light through the pattern generating optical element. In someapplications, the pattern generating optical element (i) utilizesdiffraction and/or refraction to generate the distribution. Optionally,the pattern generating optical element has a light throughput efficiencyof at least 90%

Further, in some applications, each camera may (a) have a field of viewof 45-120 degrees. The camera(s) may include a camera sensor andobjective optics including one or more lenses. In some applications, thecamera(s) may be configured to focus at an object focal plane that islocated between 1 mm and 30 mm from the lens that is farthest from thecamera sensor.

For some applications, each of the one or more cameras is configured tofocus at an object focal plane that is located between 5 mm and 11 mmfrom the lens that is farthest from the camera sensor.

For some applications, the pattern generating optical element of each ofthe one or more projectors is configured to generate the distribution ofdiscrete unconnected spots of light at all planes located between 4 mmand 24 mm from the pattern generating optical element when the lightsource (e.g., laser diode) is activated to transmit light through thepattern generating optical element.

For some applications, each of the one or more cameras is configured tofocus at an object focal plane that is located between 4 mm and 24 mmfrom the lens that is farthest from the camera sensor.

For some applications, each of the structured light projectors has afield of illumination of 70-100 degrees.

For some applications, each of the cameras has a field of view of 70-100degrees.

For some applications, each of the cameras has a field of view of 80-90degrees.

For some applications, the apparatus further includes at least oneuniform light projector, configured to project white light onto anobject being scanned, and at least one of the cameras is configured tocapture two-dimensional color images of the object using illuminationfrom the uniform light projector.

For some applications, the beam shaping optical element includes acollimating lens.

For some applications, the structured light projectors and the camerasare positioned such that each structured light projector faces an objectoutside of the wand placed in its field of illumination. Optionally,each camera may face an object outside of the wand placed in its fieldof view. Further, in some applications, at least 20% of the discreteunconnected spots of light are in the field of view of at least one ofthe cameras.

For some applications, a height of the probe is 10-15 mm, wherein lightenters the probe through a lower surface (or sensing surface) of theprobe and the height of the probe is measured from the lower surface ofthe probe to an upper surface of the probe opposite the lower surface.

For some applications, the one or more structured light projectors isexactly one structured light projector, and the one or more cameras isexactly one camera.

For some applications, the pattern generating optical element includes adiffractive optical element (DOE).

For some applications, each DOE is configured to generate thedistribution of discrete unconnected spots of light such that when thelight source is activated to transmit light through the DOE, a ratio ofilluminated area to non-illuminated area for each orthogonal plane inthe field of illumination is 1:150-1:16.

For some applications, each DOE is configured to generate thedistribution of discrete unconnected spots of light such that when thelight source is activated to transmit light through the DOE, a ratio ofilluminated area to non-illuminated area for each orthogonal plane inthe field of illumination is 1:64-1:36.

For some applications, the one or more structured light projectors are aplurality of structured light projectors. In some applications, everyspot generated by a specific DOE has the same shape. Optionally, theshape of the spots generated by at least one DOE is different from theshape of the spots generated from at least one other DOE.

For some applications, each of the one or more projectors comprises anoptical element disposed between the beam shaping optical element andthe DOE, the optical element being configured to generate a Bessel beamwhen the laser diode is activated to transmit light through the opticalelement, such that the discrete unconnected spots of light maintain adiameter of less than 0.06 mm through each inner surface of a spherethat is centered at the DOE and has a radius of between 1 mm and 30 mm.

For some applications, the optical element is configured to generate theBessel beam when the laser diode is activated to transmit light throughthe optical element, such that the discrete unconnected spots of lightmaintain a diameter of less than 0.02 mm through each inner surface of ageometric sphere that is centered at the DOE and has a radius between 1mm and 30 mm.

For some applications, each of the one or more projectors includes anoptical element disposed between the beam shaping optical element andthe DOE. The optical element may be configured to generate a Bessel beamwhen the light source is activated to transmit light through the opticalelement, such that the discrete unconnected spots of light maintain asmall diameter through a depth range. For example, in some applications,the discrete unconnected spots of light may maintain a diameter of lessthan 0.06 mm through each orthogonal plane located between 1 mm and 30mm from the DOE.

For some applications, the optical element is configured to generate aBessel beam when the laser diode is activated to transmit light throughthe optical element, such that the discrete unconnected spots of lightmaintain a diameter of less than 0.02 mm through each orthogonal planelocated between 1 mm and 30 mm from the DOE.

For some applications, the optical element is configured to generate aBessel beam when the light source is activated to transmit light throughthe optical element, such that the discrete unconnected spots of lightmaintain a diameter of less than 0.04 mm through each orthogonal planelocated between 4 mm and 24 mm from the DOE.

For some applications, the optical element is an axicon lens.

For some applications, the axicon lens is a diffractive axicon lens.

For some applications, the optical element is an annular aperture.

For some applications, the one or more structured light projectors are aplurality of structured light projectors, and the light sources of atleast two of the structured light projectors are configured to transmitlight at two distinct wavelengths, respectively.

For some applications, the light sources of at least three of thestructured light projectors are configured to transmit light at threedistinct wavelengths, respectively.

For some applications, the light sources of at least three of thestructured light projectors are configured to transmit red, blue, andgreen light, respectively.

In some applications, the light sources comprise laser diodes.

For some applications, the one or more cameras are a plurality ofcameras which are coupled to the rigid structure such that an anglebetween two respective optical axes of at least two of the cameras is0-90 degrees.

For some applications, the angle between two respective optical axes ofat least two of the cameras is 0-35 degrees.

For some applications, the one or more structured light projectors are aplurality of structured light projectors, which are coupled to the rigidstructure such that an angle between two respective optical axes of atleast two of the structured light projectors is 0-90 degrees.

For some applications, the angle between two respective optical axes ofat least two of the structured light projectors is 0-35 degrees.

For some applications, each camera has a plurality of discrete presetfocus positions, in each focus position the camera being configured tofocus at a respective object focal plane.

For some applications, each camera includes an autofocus actuatorconfigured to select a focus position from the discrete preset focuspositions.

For some applications, each of the one or more cameras includes anoptical aperture phase mask configured to extend a depth of focus of thecamera such that images formed by each camera are maintained focusedover all object distances located between 1 mm and 30 mm from the lensthat is farthest from the camera sensor.

For some applications, the optical aperture phase mask is configured toextend the depth of focus of the camera such that the images formed byeach camera are maintained focused over all object distances locatedbetween 4 mm and 24 mm from the lens that is farthest from the camerasensor.

For some applications, each of the one or more cameras is configured tocapture images at a frame rate of 30-200 frames per second.

For some applications, each of the one or more cameras is configured tocapture images at a frame rate of at least 75 frames per second.

For some applications, each of the one or more cameras is configured tocapture images at a frame rate of at least 100 frames per second.

For some applications, the laser diode of each of the one or moreprojectors is configured to transmit an elliptical beam of light. A beamshaping optical element of each of the one or more projectors mayinclude a collimating lens. Optionally, the pattern generating opticalelement includes a diffractive optical element (DOE) that is segmentedinto a plurality of sub-DOE patches arranged in an array. Each sub-DOEpatch may generate a respective distribution of discrete unconnectedspots of light in a different area of the field of illumination suchthat the distribution of discrete unconnected spots of light isgenerated when the light source is activated to transmit light throughthe segmented DOE.

For some applications, a collimating lens may be configured to generatean elliptical beam of light having a long axis of 500-700 microns and ashort axis of 100-200 microns.

For some applications, the array of sub-DOE patches may be positioned tobe contained within the elliptical beam of light when the laser diode isactivated to transmit light through the segmented DOE.

For some applications, a cross-section of each of the sub-DOE patches isa square having a side of length 30-75 microns, the cross-section beingtaken perpendicular to the optical axis of the DOE.

For some applications, the plurality of sub-DOE patches are arranged ina rectangular array including 16-72 sub-DOE patches and having a longestdimension of 500-800 microns.

For some applications, the collimating lens and the segmented DOE are asingle optical element, a first side of the optical element includingthe collimating lens, and a second side of the optical element, oppositethe first side, including the segmented DOE.

For some applications, the at least one light source of each of the oneor more projectors is a plurality of laser diodes. In some applications,the plurality of laser diodes may be configured to transmit light at thesame wavelength.

For some applications, the plurality of laser diodes may be configuredto transmit light at different wavelengths.

For some applications, the plurality of laser diodes is two laserdiodes, the two laser diodes being configured to transmit light at twodistinct wavelengths, respectively.

For some applications, the plurality of laser diodes is three laserdiodes, the three laser diodes being configured to transmit light atthree distinct wavelengths, respectively.

For some applications, the three laser diodes are configured to transmitred, blue, and green light, respectively.

For some applications:

the beam shaping optical element of each of the one or more projectorsincludes a collimating lens, and the pattern generating optical elementincludes a compound diffractive periodic structure having a periodicstructure feature size of 100-400 nm.

For some applications, the collimating lens and the compound diffractiveperiodic structure are a single optical element, a first side of theoptical element including the collimating lens, and a second side of theoptical element, opposite the first side, including the compounddiffractive periodic structure.

For some applications, the apparatus further includes an axicon lensdisposed between the collimating lens and the compound diffractiveperiodic structure, the axicon lens having an axicon head angle of 0.2-2degrees.

For some applications, the collimating lens has a focal length of 1.2-2mm.

For some applications:

the beam shaping optical element of each of the one or more projectorsincludes a collimating lens, and

the pattern generating optical element includes a micro-lens arrayhaving a numerical aperture of 0.2-0.7.

For some applications, the micro-lens array is a hexagonal micro-lensarray.

For some applications, the micro-lens array is a rectangular micro-lensarray.

For some applications, the collimating lens and the micro-lens array area single optical element, a first side of the optical element includingthe collimating lens, and a second side of the optical element, oppositethe first side, including the micro-lens array.

For some applications, the apparatus further includes an axicon lensdisposed between the collimating lens and the micro-lens array, theaxicon lens having an axicon head angle of 0.2-2 degrees.

For some applications, the collimating lens has a focal length of 1.2-2mm.

For some applications:

the beam shaping optical element of each of the one or more projectorsincludes a collimating lens, the collimating lens having a focal lengthof 1.2-2 mm,

each of the one or more projectors includes an aperture ring disposedbetween the collimating lens and the pattern generating optical element,and the pattern generating optical element includes a compounddiffractive periodic structure having a periodic structure feature sizeof 100-400 nm.

For some applications:

the beam shaping optical element of each of the one or more projectorsincludes a lens (a) disposed between the laser diode and the patterngenerating optical element, and (b) having a planar surface on a firstside of the lens and an aspherical surface on a second side of the lensopposite the first side, the aspherical surface being configured togenerate a Bessel beam directly from a diverging beam of light when thelaser diode is activated to transmit a diverging beam of light throughthe lens and the pattern generating optical element, such that thediscrete unconnected spots of light have a substantially uniform size atany orthogonal plane located between 1 mm and 30 mm from the patterngenerating optical element.

For some applications, the aspherical surface of the lens is configuredto generate a Bessel beam directly from a diverging beam of light whenthe laser diode is activated to transmit a diverging beam of lightthrough the lens and the pattern generating optical element, such thatthe discrete unconnected spots of light have a substantially uniformsize at any orthogonal plane located between 4 mm and 24 mm from thepattern generating optical element.

For some applications, the pattern generating optical element includes acompound diffractive periodic structure having a periodic structurefeature size of 100-400 nm.

For some applications, the pattern generating optical element includes amicro-lens array having a numerical aperture of 0.2-0.7.

For some applications:

(a) the beam shaping optical element includes an aspherical surface on afirst side of a lens, and (b) a planar surface on a second side of thelens, opposite the first side, is shaped to define the patterngenerating optical element, and

the aspherical surface is configured to generate a Bessel beam directlyfrom a diverging beam of light when the laser diode is activated totransmit a diverging beam of light through the lens, such that theBessel beam is split into an array of discrete Bessel beams when thelaser diode is activated to transmit the diverging beam of light throughthe lens, such that the discrete unconnected spots of light have asubstantially uniform size at all planes located between 1 mm and 30 mmfrom the lens.

For some applications, the planar surface of the lens is shaped todefine the pattern generating optical element such that the Bessel beamis split into an array of discrete Bessel beams when the laser diode isactivated to transmit the diverging beam of light through the lens, suchthat the discrete unconnected spots of light have a substantiallyuniform size at all planes located between 4 mm and 24 mm from thepattern generating optical element.

For some applications, the apparatuses and methods may further include:

at least one temperature sensor coupled to the rigid structure andconfigured to measure a temperature of the rigid structure; and

a temperature control unit.

Temperature control circuitry may be configured to (a) receive data fromthe temperature sensor indicative of the temperature of the rigidstructure, and (b) activate the temperature control unit based on thereceived data. The temperature control unit and circuitry may beconfigured to keep the probe and/or rigid structure at a temperaturebetween 35 and 43 degrees Celsius

For some applications, the temperature control unit is configured tokeep the probe at a temperature between 37 and 41 degrees Celsius.

For some applications, the temperature control unit is configured tokeep the temperature of the probe from varying by more than a thresholdtemperature change.

For some applications, the apparatus further includes:

a target such as a diffuse reflector including a plurality of regionsdisposed within the probe such that:

-   -   (a) each projector has at least one region of the diffuse        reflector in its field of illumination,    -   (b) each camera has at least one region of the diffuse reflector        in its field of view, and    -   (c) a plurality of the regions of the diffuse reflector are in        the field of view of one of the cameras and in the field of        illumination of one of the projectors.

In some applications, temperature control circuitry may be configured to(a) receive data from the cameras indicative of a position of thediffuse reflector with respect to the distribution of discreteunconnected spots of light, (b) compare the received data to a storedcalibration position of the diffuse reflector, a discrepancy between (i)the received data indicative of the position of the diffuse reflectorand (ii) the stored calibration position of the diffuse reflectorindicating a change in temperature of the probe, and (c) regulate atemperature of the probe based on the comparison of the received dataand the stored calibration position of the diffuse reflector.

There is further provided, in accordance with some applications of thepresent invention, a method for generating a digital three-dimensionalimage, the method including:

driving each one of one or more structured light projectors to project adistribution of discrete unconnected spots of light on an intraoralthree-dimensional surface;

driving each one of one or more cameras to capture an image, the imageincluding at least one of the spots, each one of the one or more camerasincluding a camera sensor including an array of pixels;

based on stored calibration values indicating (a) a camera raycorresponding to each pixel on the camera sensor of each one of the oneor more cameras, and (b) a projector ray corresponding to each of theprojected spots of light from each one of the one or more projectors,whereby each projector ray corresponds to a respective path of pixels onat least one of the camera sensors:

using a processor, running a correspondence algorithm to:

-   -   (1) for each projector ray i, identify for each detected spot j        on a camera sensor path corresponding to ray i, how many other        cameras, on their respective camera sensor paths corresponding        to ray i, detected respective spots k corresponding to        respective camera rays that intersect ray i and the camera ray        corresponding to detected spot j,        -   whereby ray i is identified as the specific projector ray            that produced a detected spot j for which the highest number            of other cameras detected respective spots k, and    -   (2) compute a respective three-dimensional position on the        intraoral three-dimensional surface at the intersection of        projector ray i and the respective camera rays corresponding to        the detected spot j and the respective detected spots k.

For some applications, running the correspondence algorithm using theprocessor further includes, following step (1), using the processor to:

remove from consideration projector ray i, and the respective camerarays corresponding to the detected spot j and the respective detectedspots k; and run the correspondence algorithm again for a next projectorray i.

For some applications, driving each one of the one or more structuredlight projectors to project a distribution of discrete unconnected spotsof light includes driving each one of the structured light projectors toproject 400-3000 discrete unconnected spots of light onto the intraoralthree-dimensional surface.

For some applications, driving each one of the one or more structuredlight projectors to project a distribution of discrete unconnected spotsof light includes driving a plurality of structured light projectors toeach project a distribution of discrete unconnected spots of light,wherein:

(a) at least two of the structured light projectors are configured totransmit light at different wavelengths, and

(b) the stored calibration values indicating a camera ray correspondingto each pixel on the camera sensor for each of the wavelengths.

For some applications, driving each one of the one or more structuredlight projectors to project a distribution of discrete unconnected spotsof light includes driving a plurality of structured light projectors toeach project a distribution of discrete unconnected spots of light,wherein every spot projected from a specific structured light projectorhas the same shape, and the shape of the spots projected from at leastone structured light projector is different from the shape of the spotsprojected from at least one other structured light projector.

For some applications, the method further includes:

driving at least one uniform light projector to project white light ontothe intraoral three-dimensional surface; and

driving at least one camera to capture two-dimensional color images ofthe intraoral three-dimensional surface using illumination from theuniform light projector.

For some applications, the method further includes, using the processorto run a surface reconstruction algorithm that combines at least oneimage captured using illumination from the structured light projectorswith a plurality of images captured using illumination from the uniformlight projector to generate a three-dimensional image of the intraoralthree-dimensional surface.

For some applications, driving each one of the one or more structuredlight projectors includes driving a plurality of structured lightprojectors to simultaneously project respective distributions ofdiscrete unconnected spots of light on the intraoral three-dimensionalsurface.

For some applications, driving each one of the one or more structuredlight projectors includes driving a plurality of structured lightprojectors to project respective discrete unconnected spots of light onthe intraoral three-dimensional surface at different respective times.

For some applications, driving the plurality of structured lightprojectors to project respective discrete unconnected spots of light onthe intraoral three-dimensional surface at different respective timesincludes driving the plurality of structured light projectors to projectrespective discrete unconnected spots of light on the intraoralthree-dimensional surface in a predetermined order.

For some applications, driving the plurality of structured lightprojectors to project respective discrete unconnected spots of light onthe intraoral three-dimensional surface at different respective timesincludes:

driving at least one structured light projector to project adistribution of discrete unconnected spots of light on the intraoralthree-dimensional surface; and determining during a scan which of aplurality of structured light projectors to next drive to project adistribution of discrete unconnected spots of light.

For some applications:

driving each one of one or more structured light projectors includesdriving exactly one structured light projector to project a distributionof discrete unconnected spots of light on an intraoral three-dimensionalsurface.

For some applications, driving each one of the one or more camerasincludes driving the one or more cameras to each capture images at aframe rate of 30-200 frames per second.

For some applications, driving the one or more cameras includes drivingthe one or more cameras to each capture images at a frame rate of atleast 75 frames per second.

For some applications, driving the one or more cameras includes drivingthe one or more cameras to each capture images at a frame rate of atleast 100 frames per second.

For some applications, using the processor includes, based on datareceived from a temperature sensor indicative of the temperature of thestructured light projectors and the cameras, selecting between aplurality of sets of stored calibration data corresponding to aplurality of respective temperatures of the structured light projectorsand the cameras, each set of stored calibration data indicating for arespective temperature (a) the projector ray corresponding to each ofthe projected spots of light from each one of the one or moreprojectors, and (b) the camera ray corresponding to each pixel on thecamera sensor of each one of the one or more cameras.

For some applications, using the processor includes, based on datareceived from a temperature sensor indicative of the temperature of thestructured light projectors and the cameras, interpolating between theplurality of sets of stored calibration data in order to obtaincalibration data for temperatures in between the respective temperaturescorresponding to each set of calibration data.

For some applications:

driving each one of the one or more cameras includes driving each one ofthe one or more cameras to capture an image further including at least aregion of a diffuse reflector having a plurality of regions such that:

-   -   (a) each projector has at least one region of the diffuse        reflector in its field of illumination,    -   (b) each camera has at least one region of the diffuse reflector        in its field of view, and    -   (c) a plurality of the regions of the diffuse reflector are in        the field of view of one of the cameras and in the field of        illumination of one of the projectors.

The processor may be used to (a) receive data from the camerasindicative of a position of the diffuse reflector with respect to thedistribution of discrete unconnected spots of light, (b) compare thereceived data to a stored calibration position of the diffuse reflector,a discrepancy between (i) the received data indicative of the positionof the diffuse reflector and (ii) the stored calibration position of thediffuse reflector indicating a shift of the projector rays and thecameras rays from their respective stored calibration values, and (c)run the correspondence algorithm based on the shift of the projectorrays and the cameras rays from their respective stored calibrationvalues.

In some embodiments, such as any of those described above or throughoutthe specification, high dynamic range 3D imaging may be provided usinglight field imaging in combination with structured illumination. Fringepatterns may be projected onto a scene and modulated by the scene depth.Then, a structured light field may be detected using light fieldrecording devices. The structured light field contains information aboutray direction and phase-encoded depth via which the scene depth can beestimated from different directions. The multidirectional depthestimation may be able to achieve high dynamic 3D imaging effectively.

Applications of the present invention may also include systems andmethods related to a three-dimensional intraoral scanning device thatincludes one or more light field cameras, and one or more patternprojectors. For example, in some embodiments, an intraoral scanningapparatus is provided. The apparatus may include an elongate handheldwand including a probe at the distal end. The probe may have a proximalend and a distal end. During an intraoral scan the probe may be placedin the oral cavity of a subject. In accordance with some applications ofthe present invention, a structured light projector and a light fieldcamera may be disposed in the proximal end of the probe, and a mirror isdisposed in the distal end of the probe. The structured light projectorand the light field camera may be positioned to face the mirror, and themirror is positioned to (a) reflect light from the structured lightprojector directly onto an object being scanned and (b) reflect lightfrom the object being scanned into the light field camera.

The structured light projector in the proximal end of the probe includesa light source. In some applications, the light source may have a fieldof illumination of at least 6 degrees and/or less than 30 degrees. Thestructured light projector may focus the light from the light source ata projector focal plane that is located at least 30 mm and/or less than140 mm from the light source. The structured light projector may furtherinclude a pattern generator, disposed in the optical path between thelight source and the projector focal plane, that generates a structuredlight pattern at the projector focal plane when the light source isactivated to transmit light through the pattern generator.

In some applications, the light field camera in the proximal end of theprobe may have a field of view of at least 6 degrees and/or less than 30degrees. The light field camera may focus at a camera focal plane thatis located at least 30 mm and/or less than 140 mm from the light fieldcamera. The light field camera may further include a light field camerasensor that includes (i) an image sensor comprising an array of sensorpixels, and (ii) an array of micro-lenses disposed in front of the imagesensor, such that each micro-lens is disposed over a sub-array of thesensor pixels. An objective lens disposed in front of the light fieldcamera sensor forms an image of the object being scanned onto the lightfield camera sensor.

In accordance with some applications of the present invention, one ormore structured light projectors and one or more light field cameras aredisposed in the distal end of the probe. The structured light projectorsand the light field cameras are positioned such that each structuredlight projector directly faces an object outside of the wand placed inits field of illumination, and each camera directly faces an objectoutside of the wand placed in its field of view. At least 40% of theprojected structured light pattern from each projector is in the fieldof view of at least one of the cameras.

The one or more structured light projectors in the distal end of theprobe each include a light source. In some applications, the respectivestructured light projectors may each have a field of illumination of atleast 60 degrees and/or less than 120 degrees. Each structured lightprojector may focus the light from the light source at a projector focalplane that is located at least 30 mm and/or less than 140 mm from thelight source. Each structured light projector may further include apattern generator disposed in the optical path between the light sourceand the projector focal plane that generates a structured light patternat the projector focal plane when the light source is activated totransmit light through the pattern generator.

In some applications, the one or more light field cameras in the distalend of the probe may each have a field of view of at least 60 degreesand/or less than 120 degrees. Each light field camera may focus at acamera focal plane that is located at least 3 mm and/or less than 40 mmfrom the light field camera. Each light field camera may further includea light field camera sensor including (i) an image sensor comprising anarray of sensor pixels, and (ii) an array of micro-lenses disposed infront of the image sensor such that each micro-lens is disposed over asub-array of the sensor pixels. An objective lens disposed in front ofeach light field camera sensor forms an image of the object beingscanned onto the light field camera sensor.

There is therefore provided, in accordance with some applications of thepresent invention, apparatus for intraoral scanning, the apparatusincluding:

(A) an elongate handheld wand including a probe at a distal end of thehandheld wand, the probe having a proximal end and a distal end;

(B) a structured light projector disposed in the proximal end of theprobe, the structured light projector:

-   -   (a) having a field of illumination of 6-30 degrees,    -   (b) including a light source, and    -   (c) configured to focus light from the light source at a        projector focal plane that is located between 30 mm and 140 mm        from the light source, and    -   (d) including a pattern generator disposed in the optical path        between the light source and the projector focal plane, and        configured to generate a structured light pattern at the        projector focal plane when the light source is activated to        transmit light through the pattern generator;

(C) a light field camera disposed in the proximal end of the probe, thelight field camera:

-   -   (a) having a field of view of 6-30 degrees,    -   (b) configured to focus at a camera focal plane that is located        between 30 mm and 140 mm from the light field camera,    -   (c) including a light field camera sensor, the light field        camera sensor including (i) an image sensor including an array        of sensor pixels, and (ii) an array of micro-lenses disposed in        front of the image sensor such that each micro-lens is disposed        over a sub-array of the sensor pixels, and    -   (d) including an objective lens disposed in front of the light        field camera sensor and configured to form an image of an object        being scanned onto the light field camera sensor; and

(D) a mirror disposed in the distal end of the handheld wand,

-   -   the structured light projector and the light field camera        positioned to face the mirror, and the mirror positioned to (a)        reflect light from the structured light projector directly onto        the object being scanned and (b) reflect light from the object        being scanned into the light field camera.

For some applications, the light source includes a light emitting diode(LED), and the pattern generator includes a mask.

For some applications, the light source includes a laser diode.

For some applications, the pattern generator includes a diffractiveoptical element (DOE) configured to generate the structured lightpattern as a distribution of discrete unconnected spots of light.

For some applications, the pattern generator includes a refractivemicro-lens array.

For some applications, a height of the probe is 14-17 mm and a width ofthe probe is 18-22 mm, the height and width defining a plane that isperpendicular to a longitudinal axis of the wand, light entering theprobe through a lower surface of the probe, and the height of the probebeing measured from the lower surface of the probe to an upper surfaceof the probe opposite the lower surface.

For some applications, the apparatus is configured for use with anoutput device, the apparatus further including:

control circuitry configured to:

-   -   (a) drive the structured light projector to project the        structured light pattern onto an object outside the wand,    -   (b) drive the light field camera to capture a light field        resulting from the structured light pattern reflecting off the        object, the light field including (i) the intensity of the        structured light pattern reflecting off of the object, and (ii)        the direction of the light rays; and at least one computer        processor configured to, based on the captured light field,        reconstruct a 3-dimensional image of the surface of the object        being scanned, and output the image to the output device.

For some applications:

(a) the object outside the wand is a tooth inside a subject's mouth,

(b) the control circuitry is configured to drive the light field camerato capture a light field resulting from the structured light patternreflecting off the tooth without the presence of a powder on the tooth,and

(c) the computer processor is configured to reconstruct a 3-dimensionalimage of the tooth based on the light field that was captured withoutthe presence of a powder on the tooth, and to output the image to theoutput device.

For some applications, each of the sub-arrays of sensor pixels in acentral region of the image sensor includes 10-40% fewer pixels thaneach of the sub-arrays of sensor pixels in a peripheral region of theimage sensor, the central region of the image sensor including at least50% of the total number of sensor pixels.

For some applications, (a) a depth at which each micro-lens disposedover a sub-array of sensor pixels in the peripheral region of the imagesensor is configured to focus is 1.1-1.4 times larger than (b) a depthat which each micro-lens disposed over a sub-array of sensor pixels inthe central region of the image sensor is configured to focus.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

(A) an elongate handheld wand including a probe at a distal end of thehandheld wand, the probe having a proximal end and a distal end;

(B) one or more structured light projectors disposed in the distal endof the probe, each structured light projector:

-   -   (a) having a field of illumination of 60-120 degrees,    -   (b) including a light source, and    -   (c) configured to focus light from the light source at a        projector focal plane that is located between 3 mm and 40 mm        from the light source, and    -   (d) including a pattern generator disposed in the optical path        between the light source and the projector focal plane, and        configured to generate a structured light pattern at the        projector focal plane when the light source is activated to        transmit light through the pattern generator; and        -   (C) one or more light field cameras disposed in the distal            end of the probe, each light field camera:    -   (a) having a field of view of 60-120 degrees,    -   (b) configured to focus at a camera focal plane that is located        between 3 mm and 40 mm from the light field camera,    -   (c) including a light field camera sensor, the light field        camera sensor including (i) an image sensor including an array        of sensor pixels, and (ii) an array of micro-lenses disposed in        front of the image sensor such that each micro-lens is disposed        over a sub-array of the sensor pixels, and    -   (d) including an objective lens disposed in front of the light        field camera sensor and configured to form an image of an object        being scanned onto the light field camera sensor,    -   the structured light projectors and the light field cameras        positioned such that (a) each structured light projector        directly faces an object outside of the wand placed in its field        of illumination, (b) each camera directly faces an object        outside of the wand placed in its field of view, and (c) at        least 40% of the structured light pattern from each projector is        in the field of view of at least one of the cameras.

For some applications, a height of the probe is 10-14 mm and a width ofthe probe is 18-22 mm, the height and width defining a plane that isperpendicular to a longitudinal axis of the wand, light entering theprobe through a lower surface of the probe, and the height of the probebeing measured from the lower surface of the probe to an upper surfaceof the probe opposite the lower surface.

For some applications, the one or more structured light projectors isexactly one structured light projector, and the one or more structuredlight field cameras is exactly one light field camera.

For some applications, the one or more structured light projectors are aplurality of structured light projectors, and the one or more lightfield cameras are a plurality of light field cameras.

For some applications, the apparatus is configured for use with anoutput device, the apparatus further including:

control circuitry configured to:

-   -   (a) drive each of the one or more structured light projectors to        project a structured light pattern onto an object outside the        wand,    -   (b) drive the one or more light field cameras to capture a light        field resulting from the structured light patterns reflecting        off the object, the light field including (i) the intensity of        the structured light pattern reflecting off of the object, (ii)        the direction of the light rays; and at least one computer        processor configured to, based on the captured light field,        reconstruct a 3-dimensional image of the surface of the object        being scanned, and output the image to the output device.

For some applications:

at least one of the one or more structured light projectors is amonochrome structured light projector configured to project a monochromestructured light pattern onto the object being scanned, at least one ofthe one or more light field cameras is a monochrome light field cameraconfigured to capture a light field resulting from the monochromestructured light pattern reflecting off the object being scanned, andthe apparatus further includes (a) a light source configured to transmitwhite light onto the object being scanned, and (b) a camera configuredto capture a 2-dimensional color image of the object being scanned.

For some applications, the monochrome structured light projector isconfigured to project the structured light pattern at a wavelength of420-470 nm.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

(A) an elongate handheld wand including a probe at a distal end of thehandheld wand, the probe having a proximal end and a distal end;

(B) a structured light projector disposed in the proximal end of theprobe, the structured light projector:

-   -   (a) having a field of illumination,    -   (b) including a light source, and    -   (c) configured to focus light from the light source at a        projector focal plane, and    -   (d) including a pattern generator disposed in the optical path        between the light source and the projector focal plane, and        configured to generate a structured light pattern at the        projector focal plane when the light source is activated to        transmit light through the pattern generator;

(C) a light field camera disposed in the proximal end of the probe, thelight field camera:

-   -   (a) having a field of view,    -   (b) configured to focus at a camera focal plane,    -   (c) including a light field camera sensor, the light field        camera sensor including (i) an image sensor including an array        of sensor pixels, and (ii) an array of micro-lenses disposed in        front of the image sensor such that each micro-lens is disposed        over a sub-array of the sensor pixels, and    -   (d) including an objective lens disposed in front of the light        field camera sensor and configured to form an image of an object        being scanned onto the light field camera sensor; and

(D) a mirror disposed in the distal end of the handheld wand,

-   -   the structured light projector and the light field camera        positioned to face the mirror, and the mirror positioned to (a)        reflect light from the structured light projector directly onto        the object being scanned and (b) reflect light from the object        being scanned into the light field camera.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

(A) an elongate handheld wand including a probe at a distal end of thehandheld wand, the probe having a proximal end and a distal end;

(B) one or more structured light projectors disposed in the distal endof the probe, each structured light projector:

-   -   (a) having a field of illumination,    -   (b) including a light source, and    -   (c) configured to focus light from the light source at a        projector focal plane, and    -   (d) including a pattern generator disposed in the optical path        between the light source and the projector focal plane, and        configured to generate a structured light pattern at the        projector focal plane when the light source is activated to        transmit light through the pattern generator; and

(C) one or more light field cameras disposed in the distal end of theprobe, each light field camera:

-   -   (a) having a field of view,    -   (b) configured to focus at a camera focal plane,    -   (c) including a light field camera sensor, the light field        camera sensor including (i) an image sensor including an array        of sensor pixels, and (ii) an array of micro-lenses disposed in        front of the image sensor such that each micro-lens is disposed        over a sub-array of the sensor pixels, and    -   (d) including an objective lens disposed in front of the light        field camera sensor and configured to form an image of an object        being scanned onto the light field camera sensor,    -   the structured light projectors and the light field cameras        positioned such that (a) each structured light projector        directly faces an object outside of the wand placed in its field        of illumination, (b) each camera directly faces an object        outside of the wand placed in its field of view, and (c) at        least 40% of the structured light pattern from each projector is        in the field of view of at least one of the cameras.

The present invention will be more fully understood from the followingdetailed description of applications thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a handheld wand with a pluralityof structured light projectors and cameras disposed within a probe at adistal end of the handheld wand, in accordance with some applications ofthe present invention;

FIGS. 2A-B are schematic illustrations of positioning configurations forthe cameras and structured light projectors respectively, in accordancewith some applications of the present invention;

FIG. 2C is a chart depicting a plurality of different configurations forthe position of the structured light projectors and the cameras in theprobe, in accordance with some applications of the present invention;

FIG. 3 is a schematic illustration of a structured light projector, inaccordance with some applications of the present invention;

FIG. 4 is a schematic illustration of a structured light projectorprojecting a distribution of discrete unconnected spots of light onto aplurality of object focal planes, in accordance with some applicationsof the present invention;

FIGS. 5A-B are schematic illustrations of a structured light projector,including a beam shaping optical element and an additional opticalelement disposed between the beam shaping optical element and a patterngenerating optical element, in accordance with some applications of thepresent invention;

FIGS. 6A-B are schematic illustrations of a structured light projectorprojecting discrete unconnected spots and a camera sensor detectingspots, in accordance with some applications of the present invention;

FIG. 7 is a flow chart outlining a method for generating a digitalthree-dimensional image, in accordance with some applications of thepresent invention;

FIG. 8 is a flowchart outlining a method for carrying out a specificstep in the method of FIG. 7, in accordance with some applications ofthe present invention;

FIGS. 9, 10, 11, and 12 are schematic illustrations depicting asimplified example of the steps of FIG. 8, in accordance with someapplications of the present invention;

FIG. 13 is a flow chart outlining further steps in the method forgenerating a digital three-dimensional image, in accordance with someapplications of the present invention;

FIGS. 14, 15, 16, and 17 are schematic illustrations depicting asimplified example of the steps of FIG. 13, in accordance with someapplications of the present invention;

FIG. 18 is a schematic illustration of the probe including a diffusereflector, in accordance with some applications of the presentinvention;

FIGS. 19A-B are schematic illustrations of a structured light projectorand a cross-section of a beam of light transmitted by a laser diode,with a pattern generating optical element shown disposed in the lightpath of the beam, in accordance with some applications of the presentinvention;

FIGS. 20A-E are schematic illustrations of a micro-lens array used as apattern generating optical element in a structured light projector, inaccordance with some applications of the present invention;

FIGS. 21A-C are schematic illustrations of a compound 2-D diffractiveperiodic structure used as a pattern generating optical element in astructured light projector, in accordance with some applications of thepresent invention;

FIGS. 22A-B are schematic illustrations showing a single optical elementthat has an aspherical first side and a planar second side, opposite thefirst side, and a structured light projector including the opticalelement, in accordance with some applications of the present invention;

FIGS. 23A-B are schematic illustrations of an axicon lens and astructured light projector including the axicon lens, in accordance withsome applications of the present invention;

FIGS. 24A-B are schematic illustrations showing an optical element thathas an aspherical surface on a first side and a planar surface on asecond side, opposite the first side, and a structured light projectorincluding the optical element, in accordance with some applications ofthe present invention;

FIG. 25 is a schematic illustration of a single optical element in astructured light projector, in accordance with some applications of thepresent invention;

FIGS. 26A-B are schematic illustrations of a structured light projectorwith more than one laser diode, in accordance with some applications ofthe present invention;

FIGS. 27A-B are schematic illustrations of different ways to combinelaser diodes of different wavelengths, in accordance with someapplications of the present invention;

FIG. 28A is a schematic illustration of a handheld wand with astructured light projector and a light field camera disposed in aproximal end of the handheld wand, and a mirror disposed within a probeat a distal end of the handheld wand, in accordance with someapplications of the present invention;

FIG. 28B is a schematic illustration of the handheld wand of FIG. 28A,with the probe shown inside a subject's mouth, in accordance with someapplications of the present invention;

FIGS. 29A-B are schematic illustrations of structured light projectors,in accordance with some applications of the present invention;

FIG. 30 is a schematic illustration of a light field camera and athree-dimensional object being captured, in accordance with someapplications of the present invention;

FIG. 31 is a schematic illustration of a handheld wand with a structuredlight projector and a light field camera disposed within a probe at thedistal end of the handheld wand, in accordance with some applications ofthe present invention; and

FIG. 32 is a schematic illustration of the handheld wand with aplurality of structured light projectors and light field camerasdisposed within the probe at the distal end of the handheld wand, inaccordance with some applications of the present invention.

DETAILED DESCRIPTION

Reference is now made to FIG. 1, which is a schematic illustration of anelongate handheld wand 20 for intraoral scanning, in accordance withsome applications of the present invention. A plurality of structuredlight projectors 22 and a plurality of cameras 24 are coupled to a rigidstructure 26 disposed within a probe 28 at a distal end 30 of thehandheld wand. In some applications, during an intraoral scan, probe 28enters the oral cavity of a subject.

For some applications, structured light projectors 22 are positionedwithin probe 28 such that each structured light projector 22 faces anobject 32 outside of handheld wand 20 that is placed in its field ofillumination, as opposed to positioning the structured light projectorsin a proximal end of the handheld wand and illuminating the object byreflection of light off a mirror and subsequently onto the object.Similarly, for some applications, cameras 24 are positioned within probe28 such that each camera 24 faces an object 32 outside of handheld wand20 that is placed in its field of view, as opposed to positioning thecameras in a proximal end of the handheld wand and viewing the object byreflection of light off a mirror and into the camera. This positioningof the projectors and the cameras within probe 28 enables the scanner tohave an overall large field of view while maintaining a low profileprobe.

In some applications, a height H1 of probe 28 is less than 15 mm, heightH1 of probe 28 being measured from a lower surface 176 (sensingsurface), through which reflected light from object 32 being scannedenters probe 28, to an upper surface 178 opposite lower surface 176. Insome applications, the height H1 is between 10-15 mm.

In some applications, cameras 24 each have a large field of view β(beta) of at least 45 degrees, e.g., at least 70 degrees, e.g., at least80 degrees, e.g., 85 degrees. In some applications, the field of viewmay be less than 120 degrees, e.g., less than 100 degrees, e.g., lessthan 90 degrees. In experiments performed by the inventors, field ofview β (beta) for each camera being between 80 and 90 degrees was foundto be particularly useful because it provided a good balance among pixelsize, field of view and camera overlap, optical quality, and cost.Cameras 24 may include a camera sensor 58 and objective optics 60including one or more lenses. To enable close focus imaging cameras 24may focus at an object focal plane 50 that is located between 1 mm and30 mm, e.g., between 4 mm and 24 mm, e.g., between 5 mm and 11 mm, e.g.,9 mm-10 mm, from the lens that is farthest from the camera sensor. Inexperiments performed by the inventors, object focal plane 50 beinglocated between 5 mm and 11 mm from the lens that is farthest from thecamera sensor was found to be particularly useful because it was easy toscan the teeth at this distance, and because most of the tooth surfacewas in good focus. In some applications, cameras 24 may capture imagesat a frame rate of at least 30 frames per second, e.g., at a frame of atleast 75 frames per second, e.g., at least 100 frames per second. Insome applications, the frame rate may be less than 200 frames persecond.

As described hereinabove, a large field of view achieved by combiningthe respective fields of view of all the cameras may improve accuracydue to reduced amount of image stitching errors, especially inedentulous regions, where the gum surface is smooth and there may befewer clear high resolution 3-D features. Having a larger field of viewenables large smooth features, such as the overall curve of the tooth,to appear in each image frame, which improves the accuracy of stitchingrespective surfaces obtained from multiple such image frames.

Similarly, structured light projectors 22 may each have a large field ofillumination a (alpha) of at least 45 degrees, e.g., at least 70degrees. In some applications, field of illumination a (alpha) may beless than 120 degrees, e.g., than 100 degrees. Further features ofstructured light projectors 22 are described hereinbelow.

For some applications, in order to improve image capture, each camera 24has a plurality of discrete preset focus positions, in each focusposition the camera focusing at a respective object focal plane 50. Eachof cameras 24 may include an autofocus actuator that selects a focusposition from the discrete preset focus positions in order to improve agiven image capture. Additionally or alternatively, each camera 24includes an optical aperture phase mask that extends a depth of focus ofthe camera, such that images formed by each camera are maintainedfocused over all object distances located between 1 mm and 30 mm, e.g.,between 4 mm and 24 mm, e.g., between 5 mm and 11 mm, e.g., 9 mm-10 mm,from the lens that is farthest from the camera sensor.

In some applications, structured light projectors 22 and cameras 24 arecoupled to rigid structure 26 in a closely packed and/or alternatingfashion, such that (a) a substantial part of each camera's field of viewoverlaps the field of view of neighboring cameras, and (b) a substantialpart of each camera's field of view overlaps the field of illuminationof neighboring projectors. Optionally, at least 20%, e.g., at least 50%,e.g., at least 75% of the projected pattern of light are in the field ofview of at least one of the cameras at an object focal plane 50 that islocated at least 4 mm from the lens that is farthest from the camerasensor. Due to different possible configurations of the projectors andcameras, some of the projected pattern may never be seen in the field ofview of any of the cameras, and some of the projected pattern may beblocked from view by object 32 as the scanner is moved around during ascan.

Rigid structure 26 may be a non-flexible structure to which structuredlight projectors 22 and cameras 24 are coupled so as to providestructural stability to the optics within probe 28. Coupling all theprojectors and all the cameras to a common rigid structure helpsmaintain geometric integrity of the optics of each structured lightprojector 22 and each camera 24 under varying ambient conditions, e.g.,under mechanical stress as may be induced by the subject's mouth.Additionally, rigid structure 26 helps maintain stable structuralintegrity and positioning of structured light projectors 22 and cameras24 with respect to each other. As further described hereinbelow,controlling the temperature of rigid structure 26 may help enablemaintaining geometrical integrity of the optics through a large range ofambient temperatures as probe 28 enters and exits a subject's oralcavity or as the subject breathes during a scan.

Reference is now made to FIGS. 2A-B, which are schematic illustration ofa positioning configuration for cameras 24 and structured lightprojectors 22 respectively, in accordance with some applications of thepresent invention. For some applications, in order to improve theoverall field of view and field of illumination of the intraoralscanner, cameras 24 and structured light projectors 22 are positionedsuch that they do not all face the same direction. For someapplications, such as is shown in FIG. 2A, a plurality of cameras 24 arecoupled to rigid structure 26 such that an angle θ (theta) between tworespective optical axes 46 of at least two cameras 24 is 90 degrees orless, e.g., 35 degrees or less. Similarly, for some applications, suchas is shown in FIG. 2B, a plurality of structured light projectors 22are coupled to rigid structure 26 such that an angle φ (phi) between tworespective optical axes 48 of at least two structured light projectors22 is 90 degrees or less, e.g., 35 degrees or less.

Reference is now made to FIG. 2C, which is a chart depicting a pluralityof different configurations for the position of structured lightprojectors 22 and cameras 24 in probe 28, in accordance with someapplications of the present invention. Structured light projectors 22are represented in FIG. 2C by circles and cameras 24 are represented inFIG. 2C by rectangles. It is noted that rectangles are used to representthe cameras, since typically, each camera sensor 58 and the field ofview β (beta) of each camera 24 have aspect ratios of 1:2. Column (a) ofFIG. 2C shows a bird's eye view of the various configurations ofstructured light projectors 22 and cameras 24. The x-axis as labeled inthe first row of column (a) corresponds to a central longitudinal axisof probe 28. Column (b) shows a side view of cameras 24 from the variousconfigurations as viewed from a line of sight that is coaxial with thecentral longitudinal axis of probe 28. Similarly to as shown in FIG. 2A,column (b) of FIG. 2C shows cameras 24 positioned so as to have opticalaxes 46 at an angle of 90 degrees or less, e.g., 35 degrees or less,with respect to each other. Column (c) shows a side view of cameras 24of the various configurations as viewed from a line of sight that isperpendicular to the central longitudinal axis of probe 28.

Typically, the distal-most (toward the positive x-direction in FIG. 2C)and proximal-most (toward the negative x-direction in FIG. 2C) cameras24 are positioned such that their optical axes 46 are slightly turnedinwards, e.g., at an angle of 90 degrees or less, e.g., 35 degrees orless, with respect to the next closest camera 24. The camera(s) 24 thatare more centrally positioned, i.e., not the distal-most camera 24 norproximal-most camera 24, are positioned so as to face directly out ofthe probe, their optical axes 46 being substantially perpendicular tothe central longitudinal axis of probe 28. It is noted that in row (xi)a projector 22 is positioned in the distal-most position of probe 28,and as such the optical axis 48 of that projector 22 points inwards,allowing a larger number of spots 33 projected from that particularprojector 22 to be seen by more cameras 24.

Typically, the number of structured light projectors 22 in probe 28 mayrange from two, e.g., as shown in row (iv) of FIG. 2C, to six, e.g., asshown in row (xii). Typically, the number of cameras 24 in probe 28 mayrange from four, e.g., as shown in rows (iv) and (v), to seven, e.g., asshown in row (ix). It is noted that the various configurations shown inFIG. 2C are by way of example and not limitation, and that the scope ofthe present invention includes additional configurations not shown. Forexample, the scope of the present invention includes more than fiveprojectors 22 positioned in probe 28 and more than seven cameraspositioned in probe 28.

In an example application, an apparatus for intraoral scanning (e.g., anintraoral scanner) includes an elongate handheld wand comprising a probeat a distal end of the elongate handheld wand, at least two lightprojectors disposed within the probe, and at least four cameras disposedwithin the probe. Each light projector may include at least one lightsource configured to generate light when activated, and a patterngenerating optical element that is configured to generate a pattern oflight when the light is transmitted through the pattern generatingoptical element. Each of the at least four cameras may include a camerasensor and one or more lenses, wherein each of the at least four camerasis configured to capture a plurality of images that depict at least aportion of the projected pattern of light on an intraoral surface. Amajority of the at least two light projectors and the at least fourcameras may be arranged in at least two rows that are each approximatelyparallel to a longitudinal axis of the probe, the at least two rowscomprising at least a first row and a second row.

In a further application, a distal-most camera along the longitudinalaxis and a proximal-most camera along the longitudinal axis of the atleast four cameras are positioned such that their optical axes are at anangle of 90 degrees or less with respect to each other from a line ofsight that is perpendicular to the longitudinal axis. Cameras in thefirst row and cameras in the second row may be positioned such thatoptical axes of the cameras in the first row are at an angle of 90degrees or less with respect to optical axes of the cameras in thesecond row from a line of sight that is coaxial with the longitudinalaxis of the probe. A remainder of the at least four cameras other thanthe distal-most camera and the proximal-most camera have optical axesthat are substantially parallel to the longitudinal axis of the probe.Each of the at least two rows may include an alternating sequence oflight projectors and cameras.

In a further application, the at least four cameras comprise at leastfive cameras, the at least two light projectors comprise at least fivelight projectors, a proximal-most component in the first row is a lightprojector, and a proximal-most component in the second row is a camera.

In a further application, the distal-most camera along the longitudinalaxis and the proximal-most camera along the longitudinal axis arepositioned such that their optical axes are at an angle of 35 degrees orless with respect to each other from the line of sight that isperpendicular to the longitudinal axis. The cameras in the first row andthe cameras in the second row may be positioned such that the opticalaxes of the cameras in the first row are at an angle of 35 degrees orless with respect to the optical axes of the cameras in the second rowfrom the line of sight that is coaxial with the longitudinal axis of theprobe.

In a further application, the at least four cameras may have a combinedfield of view of 25-45 mm along the longitudinal axis and a field ofview of 20-40 mm along a z-axis corresponding to distance from theprobe.

Reference is now made to FIG. 3, which is a schematic illustration of astructured light projector 22, in accordance with some applications ofthe present invention. In some applications, structured light projectors22 include a laser diode 36, a beam shaping optical element 40, and apattern generating optical element 38 that generates a distribution 34of discrete unconnected spots of light (further discussed hereinbelowwith reference to FIG. 4). In some applications, the structured lightprojectors 22 may be configured to generate a distribution 34 ofdiscrete unconnected spots of light at all planes located between mm and30 mm, e.g., between 4 mm and 24 mm, from pattern generating opticalelement 38 when laser diode 36 transmits light through patterngenerating optical element 38. For some applications, distribution 34 ofdiscrete unconnected spots of light is in focus at one plane locatedbetween 1 mm and 30 mm, e.g., between 4 mm and 24 mm, yet all otherplanes located between 1 mm and 30 mm, e.g., between 4 mm and 24 mm,still contain discrete unconnected spots of light. While described aboveas using laser diodes, it should be understood that this is an exemplaryand non-limiting application. Other light sources may be used in otherapplications. Further, while described as projecting a pattern ofdiscrete unconnected spots of light, it should be understood that thisis an exemplary and non-limiting application. Other patterns or arraysof lights may be used in other applications, including but not limitedto, lines, grids, checkerboards, and other arrays.

Pattern generating optical element 38 may be configured to have a lightthroughput efficiency (i.e., the fraction of light that goes into thepattern out of the total light falling on pattern generating opticalelement 38) of at least 80%, e.g., at least 90%.

For some applications, respective laser diodes 36 of respectivestructured light projectors 22 transmit light at different wavelengths,i.e., respective laser diodes 36 of at least two structured lightprojectors 22 transmit light at two distinct wavelengths, respectively.For some applications, respective laser diodes 36 of at least threestructured light projectors 22 transmit light at three distinctwavelengths respectively. For example, red, blue, and green laser diodesmay be used. For some applications, respective laser diodes 36 of atleast two structured light projectors 22 transmit light at two distinctwavelengths respectively. For example, in some applications there aresix structured light projectors 22 disposed within probe 28, three ofwhich contain blue laser diodes and three of which contain green laserdiodes.

Reference is now made to FIG. 4, which is a schematic illustration of astructured light projector 22 projecting a distribution of discreteunconnected spots of light onto a plurality of object focal planes, inaccordance with some applications of the present invention. Object 32being scanned may be one or more teeth or other intraoral object/tissueinside a subject's mouth. The somewhat translucent and glossy propertiesof teeth may affect the contrast of the structured light pattern beingprojected. For example, (a) some of the light hitting the teeth mayscatter to other regions within the intraoral scene, causing an amountof stray light, and (b) some of the light may penetrate the tooth andsubsequently come out of the tooth at any other point. Thus, in order toimprove image capture of an intraoral scene under structured lightillumination, without using contrast enhancement means such as coatingthe teeth with an opaque powder, the inventors have realized that asparse distribution 34 of discrete unconnected spots of light mayprovide an improved balance between reducing the amount of projectedlight while maintaining a useful amount of information. The sparsenessof distribution 34 may be characterized by a ratio of:

(a) illuminated area on an orthogonal plane 44 in field of illuminationa (alpha), i.e., the sum of the area of all projected spots 33 on theorthogonal plane 44 in field of illumination a (alpha), to

(b) non-illuminated area on orthogonal plane 44 in field of illuminationa (alpha). In some applications, sparseness ratio may be at least 1:150and/or less than 1:16 (e.g., at least 1:64 and/or less than 1:36).

In some applications, each structured light projector 22 projects atleast 400 discrete unconnected spots 33 onto an intraoralthree-dimensional surface during a scan. In some applications, eachstructured light projector 22 projects less than 3000 discreteunconnected spots 33 onto an intraoral surface during a scan. In orderto reconstruct the three-dimensional surface from projected sparsedistribution 34, correspondence between respective projected spots 33and the spots detected by cameras 24 must be determined, as furtherdescribed hereinbelow with reference to FIGS. 7-19.

For some applications, pattern generating optical element 38 is adiffractive optical element (DOE) 39 (FIG. 3) that generatesdistribution 34 of discrete unconnected spots 33 of light when laserdiode 36 transmits light through DOE 39 onto object 32. As used hereinthroughout the present application, including in the claims, a spot oflight is defined as a small area of light having any shape. For someapplications, respective DOE's 39 of different structured lightprojectors 22 generate spots having different respective shapes, i.e.,every spot 33 generated by a specific DOE 39 has the same shape, and theshape of spots 33 generated by at least one DOE 39 is different from theshape of spots 33 generated by at least one other DOE 39. By way ofexample, some of DOE's 39 may generate circular spots 33 (such as isshown in FIG. 4), some of DOE's 39 may generate square spots, and someof the DOE's 39 may generate elliptical spots. Optionally, some DOE's 39may generate line patterns, connected or unconnected.

Reference is now made to FIGS. 5A-B, which are schematic illustrationsof a structured light projector 22, including beam shaping opticalelement 40 and an additional optical element disposed between beamshaping optical element 40 and pattern generating optical element 38,e.g., DOE 39, in accordance with some applications of the presentinvention. Optionally, beam shaping optical element 40 is a collimatinglens 130. Collimating lens 130 may be configured to have a focal lengthof less than 2 mm. Optionally, the focal length may be at least at least1.2 mm.

For some applications, an additional optical element 42, disposedbetween beam shaping optical element 40 and pattern generating opticalelement 38, e.g., DOE 39, generates a Bessel beam when laser diode 36transmits light through optical element 42. In some applications, theBessel beam is transmitted through DOE 39 such that all discreteunconnected spots 33 of light maintain a small diameter (e.g., less than0.06 mm, e.g., less than 0.04 mm, e.g., less than 0.02 mm), through arange of orthogonal planes 44 (e.g., each orthogonal plane locatedbetween 1 mm and 30 mm from DOE 39, e.g., between 4 mm and 24 mm fromDOE 39, etc.). The diameter of spots 33 is defined, in the context ofthe present patent application, by the full width at half maximum (FWHM)of the intensity of the spot.

Notwithstanding the above description of all spots being smaller than0.06 mm, some spots that have a diameter near the upper end of theseranges (e.g., only somewhat smaller than 0.06 mm, or 0.02 mm) that arealso near the edge of the field of illumination of a projector 22 may beelongated when they intersect a geometric plane that is orthogonal toDOE 39. For such cases, it is useful to measure their diameter as theyintersect the inner surface of a geometric sphere that is centered atDOE 39 and that has a radius between 1 mm and 30 mm, corresponding tothe distance of the respective orthogonal plane that is located between1 mm and 30 mm from DOE 39. As used throughout the present application,including in the claims, the word “geometric” is taken to relate to atheoretical geometric construct (such as a plane or a sphere), and isnot part of any physical apparatus.

For some applications, when the Bessel beam is transmitted through DOE39, spots 33 having diameters larger than 0.06 mm are generated inaddition to the spots having diameters less than 0.06 mm.

For some applications, optical element 42 is an axicon lens 45, such asis shown in FIG. 5A and further described hereinbelow with reference toFIGS. 23A-B. Alternatively, optical element 42 may be an annularaperture ring 47, such as is shown in FIG. 5B. Maintaining a smalldiameter of the spots improves 3-D resolution and precision throughoutthe depth of focus. Without optical element 42, e.g., axicon lens 45 orannular aperture ring 47, the spot of spots 33 size may vary, e.g.,becomes bigger, as you move farther away from a best focus plane due todiffraction and defocus.

Reference is now made to FIGS. 6A-B, which are schematic illustrationsof a structured light projector 22 projecting discrete unconnected spots33 and a camera sensor 58 detecting spots 33′, in accordance with someapplications of the present invention. For some applications, a methodis provided for determining correspondence between the projected spots33 on the intraoral surface and detected spots 33′ on respective camerasensors 58. Once the correspondence is determined, a three-dimensionalimage of the surface is reconstructed. Each camera sensor 58 has anarray of pixels, for each of which there exists a corresponding cameraray 86. Similarly, for each projected spot 33 from each projector 22there exists a corresponding projector ray 88. Each projector ray 88corresponds to a respective path 92 of pixels on at least one of camerasensors 58. Thus, if a camera sees a spot 33′ projected by a specificprojector ray 88, that spot 33′ will necessarily be detected by a pixelon the specific path 92 of pixels that corresponds to that specificprojector ray 88. With specific reference to FIG. 6B, the correspondencebetween respective projector rays 88 and respective camera sensor paths92 is shown. Projector ray 88′ corresponds to camera sensor path 92′,projector ray 88″ corresponds to camera sensor path 92″, and projectorray 88′″ corresponds to camera sensor path 92′″. For example, if aspecific projector ray 88 were to project a spot into a dust-filledspace, a line of dust in the air would be illuminated. The line of dustas detected by camera sensor 58 would follow the same path on camerasensor 58 as the camera sensor path 92 that corresponds to the specificprojector ray 88.

During a calibration process, calibration values are stored based oncamera rays 86 corresponding to pixels on camera sensor 58 of each oneof cameras 24, and projector rays 88 corresponding to projected spots 33of light from each structured light projector 22. For example,calibration values may be stored for (a) a plurality of camera rays 86corresponding to a respective plurality of pixels on camera sensor 58 ofeach one of cameras 24, and (b) a plurality of projector rays 88corresponding to a respective plurality of projected spots 33 of lightfrom each structured light projector 22.

By way of example, the following calibration process may be used. A highaccuracy dot target, e.g., black dots on a white background, isilluminated from below and an image is taken of the target with all thecameras. The dot target is then moved perpendicularly toward thecameras, i.e., along the z-axis, to a target plane. The dot-centers arecalculated for all the dots in all respective z-axis positions to createa three-dimensional grid of dots in space. A distortion and camerapinhole model is then used to find the pixel coordinate for eachthree-dimensional position of a respective dot-center, and thus a cameraray is defined for each pixel as a ray originating from the pixel whosedirection is towards a corresponding dot-center in the three-dimensionalgrid. The camera rays corresponding to pixels in between the grid pointscan be interpolated. The above-described camera calibration procedure isrepeated for all respective wavelengths of respective laser diodes 36,such that included in the stored calibration values are camera rays 86corresponding to each pixel on each camera sensor 58 for each of thewavelengths.

After cameras 24 have been calibrated and all camera ray 86 valuesstored, structured light projectors 22 may be calibrated as follows. Aflat featureless target is used and structured light projectors 22 areturned on one at a time. Each spot is located on at least one camerasensor 58. Since cameras 24 are now calibrated, the three-dimensionalspot location of each spot is computed by triangulation based on imagesof the spot in multiple different cameras. The above-described processis repeated with the featureless target located at multiple differentz-axis positions. Each projected spot on the featureless target willdefine a projector ray in space originating from the projector.

Reference is now made to FIG. 7, which is a flow chart outlining amethod for generating a digital three-dimensional image, in accordancewith some applications of the present invention. In steps 62 and 64,respectively, of the method outlined by FIG. 7 each structured lightprojector 22 is driven to project distribution 34 of discreteunconnected spots 33 of light on an intraoral three-dimensional surface,and each camera 24 is driven to capture an image that includes at leastone of spots 33. Based on the stored calibration values indicating (a) acamera ray 86 corresponding to each pixel on camera sensor 58 of eachcamera 24, and (b) a projector ray 88 corresponding to each projectedspot 33 of light from each structured light projector 22, acorrespondence algorithm is run in step 66 using a processor 96 (FIG.1), further described hereinbelow with reference to FIGS. 8-12. Once thecorrespondence is solved, three-dimensional positions on the intraoralsurface are computed in step 68 and used to generate a digitalthree-dimensional image of the intraoral surface. Furthermore, capturingthe intraoral scene using multiple cameras 24 provides a signal to noiseimprovement in the capture by a factor of the square root of the numberof cameras.

Reference is now made to FIG. 8, which is a flowchart outlining thecorrespondence algorithm of step 66 in FIG. 7, in accordance with someapplications of the present invention. Based on the stored calibrationvalues, all projector rays 88 and all camera rays 86 corresponding toall detected spots 33′ are mapped (step 70), and all intersections 98(FIG. 10) of at least one camera ray 86 and at least one projector ray88 are identified (step 72). FIGS. 9 and 10 are schematic illustrationsof a simplified example of steps 70 and 72 of FIG. 8, respectively. Asshown in FIG. 9, three projector rays 88 are mapped along with eightcamera rays 86 corresponding to a total of eight detected spots 33′ oncamera sensors 58 of cameras 24. As shown in FIG. 10, sixteenintersections 98 are identified.

In steps 74 and 76 of FIG. 7, processor 96 determines a correspondencebetween projected spots 33 and detected spots 33′ so as to identify athree-dimensional location for each projected spot 33 on the surface.FIG. 11 is a schematic illustration depicting steps 74 and 76 of FIG. 8using the simplified example described hereinabove in the immediatelypreceding paragraph. For a given projector ray i, processor 96 “looks”at the corresponding camera sensor path 90 on camera sensor 58 of one ofcameras 24. Each detected spot j along camera sensor path 90 will have acamera ray 86 that intersects given projector ray i, at an intersection98. Intersection 98 defines a three-dimensional point in space.Processor 96 then “looks” at camera sensor paths 90′ that correspond togiven projector ray i on respective camera sensors 58′ of other cameras24, and identifies how many other cameras 24, on their respective camerasensor paths 90′ corresponding to given projector ray i, also detectedrespective spots k whose camera rays 86′ intersect with that samethree-dimensional point in space defined by intersection 98. The processis repeated for all detected spots j along camera sensor path 90, andthe spot j for which the highest number of cameras 24 “agree,” isidentified as the spot 33 (FIG. 12) that is being projected onto thesurface from given projector ray i. That is, projector ray i isidentified as the specific projector ray 88 that produced a detectedspot j for which the highest number of other cameras detected respectivespots k. A three-dimensional position on the surface is thus computedfor that spot 33.

For example, as shown in FIG. 11, all four of the cameras detectrespective spots, on their respective camera sensor paths correspondingto projector ray i, whose respective camera rays intersect projector rayi at intersection 98, intersection 98 being defined as the intersectionof camera ray 86 corresponding to detected spot j and projector ray i.Hence, all four cameras are said to “agree” on there being a spot 33projected by projector ray i at intersection 98. When the process isrepeated for a next spot j′, however, none of the other cameras detectrespective spots, on their respective camera sensor paths correspondingto projector ray i, whose respective camera rays intersect projector rayi at intersection 98′, intersection 98′ being defined as theintersection of camera ray 86″ (corresponding to detected spot j′) andprojector ray i. Thus, only one camera is said to “agree” on there beinga spot 33 projected by projector ray i at intersection 98′, while fourcameras “agree” on there being a spot 33 projected by projector ray i atintersection 98. Projector ray i is therefore identified as being thespecific projector ray 88 that produced detected spot j, by projecting aspot 33 onto the surface at intersection 98 (FIG. 12). As per step 78 ofFIG. 8, and as shown in FIG. 12, a three-dimensional position 35 on theintraoral surface is computed at intersection 98.

Reference is now made to FIG. 13, which is a flow chart outliningfurther steps in the correspondence algorithm, in accordance with someapplications of the present invention. Once position 35 on the surfaceis determined, projector ray i that projected spot j, as well as allcamera rays 86 and 86′ corresponding to spot j and respective spots kare removed from consideration (step 80) and the correspondencealgorithm is run again for a next projector ray i (step 82). FIG. 14depicts the simplified example described hereinabove after the removalof the specific projector ray i that projected spot 33 at position 35.As per step 82 in the flow chart of FIG. 13, the correspondencealgorithm is then run again for a next projector ray i. As shown in FIG.14, the remaining data show that three of the cameras “agree” on therebeing a spot 33 at intersection 98, intersection 98 being defined by theintersection of camera ray 86 corresponding to detected spot j andprojector ray i. Thus, as shown in FIG. 15, a three-dimensional position37 is computed at intersection 98.

As shown in FIG. 16, once three-dimensional position 37 on the surfaceis determined, again projector ray i that projected spot j, as well asall camera rays 86 and 86′ corresponding to spot j and respective spotsk are removed from consideration. The remaining data show a spot 33projected by projector ray i at intersection 98, and a three-dimensionalposition 41 on the surface is computed at intersection 98. As shown inFIG. 17, according to the simplified example, the three projected spots33 of the three projector rays 88 of structured light projector 22 havenow been located on the surface at three-dimensional positions 35, 37,and 41. In some applications, each structured light projector 22projects 400-3000 spots 33. Once correspondence is solved for allprojector rays 88, a reconstruction algorithm may be used to reconstructa digital image of the surface using the computed three-dimensionalpositions of the projected spots 33.

Reference is again made to FIG. 1. For some applications, there is atleast one uniform light projector 118 coupled to rigid structure 26.Uniform light projector 118 transmits white light onto object 32 beingscanned. At least one camera, e.g., one of cameras 24, capturestwo-dimensional color images of object 32 using illumination fromuniform light projector 118. Processor 96 may run a surfacereconstruction algorithm that combines at least one image captured usingillumination from structured light projectors 22 with a plurality ofimages captured using illumination from uniform light projector 118 inorder to generate a digital three-dimensional image of the intraoralthree-dimensional surface. Using a combination of structured light anduniform illumination enhances the overall capture of the intraoralscanner and may help reduce the number of options that processor 96needs to consider when running the correspondence algorithm.

For some applications, structured light projectors 22 are simultaneouslydriven to project their respective distributions 34 of discreteunconnected spots 33 of light on the intraoral three-surface.Alternatively, structured light projectors 22 may be driven to projecttheir respective distributions 34 of discrete unconnected spots 33 oflight on the intraoral three-surface at different respective times,e.g., in a predetermined order, or in an order that is dynamicallydetermined during a scan. Alternatively, for some applications, a singlestructured light projector 22 may be driven to project distribution 34.

Dynamically determining which structured light projectors 22 to activateduring a scan may improve overall signal quality of the scan as some ofthe structured light projectors may have better signal quality in someregions of the intraoral cavity relative to other regions. For example,when scanning a subject's palate (upper jaw region) the red projectorstend to have better signal quality than the blue projectors.Additionally, hard-to-see regions within the intraoral cavity may beencountered during a scan, e.g., an area with missing teeth or narrowcracks between big teeth. In these types of cases, dynamicallydetermining which structured light projector 22 to activate during ascan allows specific projectors that may have better line of sight tothe region in question to be activated.

For some applications, different structured light projectors 22 may beconfigured to focus at different object focal planes. Dynamicallydetermining which structured light projectors 22 to activate during ascan allows for activating specific structured light projectors 22according to their respective object focal planes depending on adistance from a region currently being scanned.

For some applications, all data points taken at a specific time are usedas a rigid point cloud, and multiple such point clouds are captured at aframe rate of over 10 captures per second. The plurality of point cloudsare then stitched together using a registration algorithm, e.g.,iterative closest point (ICP), to create a dense point cloud. A surfacereconstruction algorithm may then be used to generate a representationof the surface of object 32.

For some applications, at least one temperature sensor 52 is coupled torigid structure 26 and measures a temperature of rigid structure 26.Temperature control circuitry 54 disposed within handheld wand 20 (a)receives data from temperature sensor 52 indicative of the temperatureof rigid structure 26 and (b) activates a temperature control unit 56 inresponse to the received data. Temperature control unit 56, e.g., a PIDcontroller, keeps probe 28 at a desired temperature (e.g., between 35and 43 degrees Celsius, between 37 and 41 degrees Celsius, etc.).Keeping probe 28 above 35 degrees Celsius, e.g., above 37 degreesCelsius, reduces fogging of the glass surface of handheld wand 20,through which structured light projectors 22 project and cameras 24view, as probe 28 enters the intraoral cavity, which is typically aroundor above 37 degrees Celsius. Keeping probe 28 below 43 degrees, e.g.,below 41 degrees Celsius, prevents discomfort or pain.

Additionally, in order for the stored calibration values of the camerarays and the projector rays to be of use during a scan, the temperatureof cameras 24 and structured light projectors 22 may be prevented fromvarying so as to maintain geometrical integrity of the optics. Avariation in temperature can cause the length of probe 28 to change dueto thermal expansion, which in turn may cause the respective camera andprojector positions to shift. Due to different types of stress that maybuild up within probe 28 during such thermal expansion, twisting canalso occur, causing the angles of the respective camera rays andprojector rays to shift as well. Within the cameras and projectors,geometric changes may occur due to temperature variation as well. Forexample, DOE 39 may expand and alter the projected pattern, temperaturevariations may affect the refractive index of the camera lenses, ortemperature variations may change the wavelengths transmitted by laserdiodes 36. Therefore, in addition to keeping probe 28 at a temperaturewithin the range described above, temperature control unit 56 mayfurther prevent the temperature of probe 28 from varying by more than 1degree when handheld wand 20 is in use, so as to maintain geometricalintegrity of the optics disposed within probe 28. For example, iftemperature control unit 56 is keeping probe 28 at a temperature of 39degrees Celsius then temperature control unit 56 will further ensurethat during use the temperature of probe 28 does not go below 38 degreesCelsius or above 40 degrees Celsius.

For some applications, probe 28 is maintained at its controlledtemperature through the use of a combination of heating and cooling. Forexample, temperature control unit 56 may include a heater, e.g., aplurality of heaters, and a cooler, e.g., a thermoelectric cooler. Ifthe temperature of probe 28 drops below degrees Celsius the heater(s)may be used to raise the temperature of probe 28, and if the temperatureof probe 28 goes above 40 degrees Celsius, the thermoelectric cooler maybe used to lower the temperature of probe 28.

Alternatively, for some applications, probe 28 is maintained at itscontrolled temperature through the use of heating only, without cooling.The use of laser diodes 36 and diffractive and/or refractive patterngenerating optical elements helps maintain an energy efficientstructured light projector so as to limit probe 28 from heating upduring use; laser diodes 36 may use less than 0.2 Watts of power whiletransmitting at a high brightness and diffractive and/or refractivepattern generating optical elements utilize all the transmitted light(in contrast, for example, to a mask which stops some of the rays fromhitting the object). External environmental temperatures, such as thoseencountered within a subject's intraoral cavity, may however causeheating of probe 28. To overcome this, heat may be drawn out of theprobe 28 via a heat conducting element 94, e.g., a heat pipe, that isdisposed within handheld wand 20, such that a distal end 95 of heatconducting element 94 is in contact with rigid structure 26 and aproximal end 99 is in contact with a proximal end 100 of handheld wand20. Heat is thereby transferred from rigid structure 26 to proximal end100 of handheld wand 20. Alternatively or additionally, a fan disposedin a handle region 174 of handheld wand 20 may be used to draw heat outof probe 28.

For some applications, alternatively or additionally to maintaininggeometric integrity of the optics by preventing the temperature of probe28 from varying by more than a threshold change in temperature,processor 96 may select between a plurality of sets of calibration datacorresponding to different temperatures respectively. For example, thethreshold change may be 1 degree Celsius. Based on data received fromtemperature sensor 52 indicative of the temperature of structured lightprojectors 22 and cameras 24, processor 96 may select between aplurality of sets of stored calibration data corresponding to aplurality of respective temperatures of structured light projectors 22and cameras 24, each set of stored calibration data indicating for arespective temperature (a) the projector ray corresponding to each ofthe projected spots of light from each one of the one or moreprojectors, and (b) the camera ray corresponding to each pixel on thecamera sensor of each one of the one or more cameras. If processor 96only has access to stored calibration data for a specific plurality oftemperatures, processor 96 may interpolate between the plurality of setsof stored calibration data based on data received from temperaturesensor 52, in order to obtain calibration data for temperatures betweenthe respective temperatures corresponding to each set of calibrationdata.

Reference is now made to FIG. 18, which is a schematic illustration ofprobe 28, in accordance with some applications of the present invention.For some applications, probe 28 further includes a target such as adiffuse reflector 170 having a plurality of regions 172 disposed withinprobe 28 (or, as shown in FIG. 18, adjacent to probe 28). In someapplications, (a) each structured light projector 22 may have at leastone region 172 of diffuse reflector 170 in its field of illumination,(b) each camera 24 has at least one region 172 of diffuse reflector 170in its field of view, and (c) a plurality of regions 172 of diffusereflector 170 are in the field of view of a camera 24 and in the fieldof illumination of a structured light projector 22. Alternatively oradditionally to maintaining geometric integrity of the optics bypreventing the temperature of probe 28 from varying by more than athreshold temperature change, processor 96 may (a) receive data fromcameras 24 indicative of the position of the diffuse reflector withrespect to distribution 34 of discrete unconnected spots 33 of light,(b) compare the received data to a stored calibration position ofdiffuse reflector 170, wherein a discrepancy between (i) the receiveddata indicative of the position of diffuse reflector 170 and (ii) thestored calibration position of diffuse reflector 170, indicates a shiftof projector rays 88 and cameras rays 86 from their respective storedcalibration values, and (c) run the correspondence algorithm based onthe shift of projector rays 88 and cameras rays 86.

Alternatively or additionally, a discrepancy between (i) the receiveddata indicative of the position of diffuse reflector 170 and (ii) thestored calibration position of diffuse reflector 170 may indicate achange in temperature of probe 28. In this case the temperature of probe28 may be regulated based on the comparison of the received data and thestored calibration position of diffuse reflector 170.

Hereinbelow is described a plurality of applications for structuredlight projectors 22.

Reference is now made to FIG. 19A-B, which are schematic illustrationsof structured light projector 22 and a cross-section of a beam 120 oflight transmitted by a laser diode 36, with a pattern generating opticalelement 38 shown disposed in the light path of the beam, in accordancewith some applications of the present invention. In some applications,each laser diode 36 transmits an elliptical beam 120 whose ellipticalcross-section has (a) a long axis of at least 500 microns and/or lessthan 700 microns and (b) a short axis of at least 100 microns and/orless than 200 microns. For some applications, a small area beam splittermay be used in order to generate a tightly focused spot array, e.g., aDOE having a side length of less than 100 microns may be used in orderto maintain projected spots 33 in tight focus over the entire focusrange of interest. However, such a small DOE would utilize only afraction of the light transmitted via elliptical laser beam 120.

Therefore, for some applications, pattern generating optical element 38is a segmented DOE 122 that is segmented into a plurality of sub-DOEpatches 124 that are arranged in an array. The array of sub-DOE patches124 is positioned so as to (a) be contained within elliptical beam 120of light and (b) utilize a high percentage, e.g., at least 50% of thelight transmitted via elliptical laser beam 120. In some applications,the array is a rectangular array including at least 16 and/or less than72 sub-DOE patches 124 and has a longest dimension of at least 500microns and/or less than 800 microns. Each sub-DOE patch 124 may have asquare cross-section having a side of length of at least 30 micronsand/or less than 75 microns, the cross-section being taken perpendicularto the optical axis of the DOE.

Each sub-DOE patch 124 generates a respective distribution 126 ofdiscrete unconnected spots 33 of light in a different area 128 of thefield of illumination. For this application of structured lightprojector 22, distribution 34 of discrete unconnected spots 33 of light,as described hereinabove with reference to FIG. 4, is a combination ofrespective distributions 126 generated by respective sub-DOE patches124. FIG. 19B shows an orthogonal plane 44, on which is shown respectivedistributions 126 of discrete unconnected spots 33 of light, eachrespective distribution 126 being in a different area 128 of the fieldof illumination. Since each sub-DOE patch 124 is responsible for adifferent area 128 of the field of illumination, each sub-DOE patch 124has a different design so as to direct its respective distribution 126in a different direction and avoid beam crossing in order to avoidoverlap between projected spots 33.

Reference is now made to FIGS. 20A-E, which are schematic illustrationsof a micro-lens array 132 as pattern generating optical element 38, inaccordance with some applications of the present invention. A micro-lensarray can be used as spot generator since it is periodic and the profilevariation of each lens in the array is in the wavelength scale. Thepitch of micro-lens array 132 is tuned for the desired angular pitchbetween the spots. The numerical aperture (NA) of micro-lens array 132is tuned to provide the desired angular field of illumination, asdescribed hereinabove. In some applications, the NA of micro-lens array132 is at least 0.2 and/or less than 0.7. Micro-lens array 132 may be,for example, a hexagonal micro-lens array, such as is shown in FIG. 20C,or a rectangular micro-lens array, such as is shown in FIG. 20E.

Structured light projectors 22 that have micro-lens array 132 as patterngenerating optical element 38 may include laser diode 36, collimatinglens 130, an aperture, and micro-lens array 132. The aperture defines asmaller input beam diameter in order to maintain tightly focused spotsat a near focal distance, e.g., at least 1 mm and/or less than 30 mm,e.g., at least 4 mm and/or less than 24 mm, from micro-lens array 132.FIG. 20B shows the collimated laser beam illuminating micro-lens array132, and micro-lens array then generating diverging beams 134 of light,the interference of these diverging beams generating an array of spots33, e.g., distribution 34 (FIG. 20D). For some applications, theaperture is a chrome film that is applied to the laser-diode-side ofcollimating lens 130. Alternatively, for some applications, the apertureis a chrome film disposed on the collimating-lens-side of micro-lensarray 132. In some applications, the aperture may span a distance of atleast 10 times the pitch of micro-lens array 132 and has a diameter ofat least 50 microns and/or less than 200 microns.

Reference is now made to FIGS. 21A-C, which are schematic illustrationsof a compound 2-D diffractive periodic structure 136, e.g., adiffractive grating such as a Dammann grating, as pattern generatingoptical element 38, in accordance with some applications of the presentinvention. Compound diffractive periodic structure 136 may have aperiodic structure feature size 137 of at least 100 nm and/or less than400 nm. The large field of illumination as described hereinabove may beobtained by small sub-features that are around 300 nm. The period ofcompound diffractive periodic structure 136 may be tuned to provide adesired angular pitch of the projected beams of light.

Structured light projectors 22 that have compound diffractive periodicstructure 136 as pattern generating optical element 38 may include laserdiode 36, collimating lens 130, an aperture, and compound diffractiveperiodic structure 136. The aperture defines a smaller input beamdiameter in order to maintain tightly focused spots at a near focaldistance, e.g., at least 1 mm and/or less than 30 mm, e.g., at least 4mm and/or less than 24 mm, from compound diffractive periodic structure136. For some applications, the aperture is chrome film that is over theperiodic structure features of compound diffractive periodic structure136. In some applications, the aperture may span a distance of at least10 periods of compound diffractive periodic structure 136 and has adiameter of at least 50 microns and/or less than 200 microns.

For some applications, beam shaping optical element 40 (such as is shownin FIG. 3) is a collimating lens 130 disposed between laser diode 36 andpattern generating optical element 38. With respect to the applicationsdescribed hereinabove with reference to FIGS. 19A-B, 20A-E, and 21A-C,collimating lens 130 may be disposed between laser diode 36 andsegmented DOE 122 (FIG. 19A), between laser diode 36 and micro-lensarray 132 (FIG. 20A), and between laser diode 36 and compounddiffractive periodic structure 136 (FIG. 21A).

Reference is now made to FIGS. 22A-B, which are schematic illustrationsshowing a single optical element 138 that has an aspherical first sideand a planar second side, opposite the first side, and structured lightprojector 22 including optical element 138, in accordance with someapplications of the present invention. For some applications,collimating lens 130 and pattern generating optical element 38 may befabricated as single optical element 138, a first aspherical side 140 ofwhich collimates the light transmitted from laser diode 36, and a secondplanar side 142 of which generates distribution 34 of discreteunconnected spots 33 of light. Planar side 142 of single optical element138 may be shaped to define DOE 39, segmented DOE 122, micro-lens array132, or compound diffractive periodic structure 136.

Reference is now made to FIGS. 23A-B, which are schematic illustrationsof an axicon lens 144 and structured light projector 22 including axiconlens 144, in accordance with some applications of the present invention.Axicon lenses are known to generate a Bessel beam, which is a beam oflight that is focused throughout a desired depth range depending on theinput beam diameter and the axicon head angle. For some applications,axicon lens 144, having a head angle γ (gamma) of at least 0.2 degreesand/or less than 2 degrees, is disposed between collimating lens 130 andpattern generating optical element 38. Axicon lens 144 generates afocused Bessel beam 146 when laser diode 36 transmits light throughaxicon lens 144. Focused Bessel beam 146 is split into many beams 148 bypattern generating optical element 38, each beam 148 being an exact copyof the Bessel beam 146 generated by axicon lens 144. Pattern generatingoptical element 38 may be DOE 39, micro-lens array 132, or compounddiffractive periodic structure 136.

Reference is now made to FIGS. 24A-B, which are schematic illustrationsshowing an optical element 150 that has an aspherical surface 152 on afirst side and a planar surface on a second side, opposite the firstside, and structured light projector 22 including optical element 150,in accordance with some applications of the present invention. For someapplications, collimating lens 130 and axicon lens 144 may be fabricatedas single optical element 150. Aspherical surface 152 of single opticalelement 150 generates a Bessel beam directly from a diverging beam oflight when laser diode 36 transmits light through optical element 150.As the light then travels through pattern generating optical element 38,distribution 34 of discrete unconnected spots 33 of light is generatedsuch that discrete unconnected spots 33 of light have a substantiallyuniform size at any orthogonal plane located between 1 mm and 30 mm,e.g., between mm and 24 mm, from pattern generating optical element 38.Pattern generating optical element 38 may be DOE 39, micro-lens array132, or compound diffractive periodic structure 136. As used hereinthroughout the present application, including in the claims, spotshaving a “substantially uniform size” means that the size of the spotsdoes not vary by more than 40%.

Reference is now made to FIG. 25, which is a schematic illustration of asingle optical element 154 in structured light projector 22, inaccordance with some applications of the present invention. For someapplications, single optical element 154 may perform the functions ofthe collimating lens, axicon lens, and pattern generating opticalelement. Single optical element 154 includes an aspherical surface 156on a first side and a planar surface 158 on a second side, opposite thefirst side. Aspherical surface 156 generates a Bessel beam directly froma diverging beam of light when laser diode 36 transmits a diverging beamof light through the single optical element 154. Planar surface 158 isshaped to define pattern generating optical element 38 and thus splitsthe Bessel beam into an array of discrete Bessel beams 160 so as togenerate distribution 34 of discrete unconnected spots 33 of light, suchthat discrete unconnected spots 33 of light have a substantially uniformsize at any orthogonal plane located between 1 mm and 30 mm, e.g.,between 4 mm and 24 mm, from pattern single optical element 154. Planarsurface 158 may be shaped to define

DOE 39, micro-lens array 132, or compound diffractive periodic structure136.

Reference is now made to FIGS. 26A-B, which are schematic illustrationsof structured light projector 22 with more than one light source (e.g.,laser diodes 36), in accordance with some applications of the presentinvention. When using a laser diode, laser speckles may give rise tospatial noise. The speckle effect is a result of interference of manywaves of the same frequency but different phases and amplitudes. Whenall added together, the resultant wave is a wave whose amplitude variesrandomly across the beam profile. For some applications, the speckleeffect may be reduced by combining a plurality of laser diodes 36 of thesame wavelength. Different lasers having the same wavelength are notcoherent to one another, so combining them into the same spatial space,or the same diffractive beam splitter 162, will lower the speckles by atleast a factor of the square root of the number of different laserdiodes 36.

Beam splitter 162 may be a standard 50/50 splitter, lowering theefficiency of both beams to under 50%, or a polarizing beam splitter(PBS), keeping the efficiency at greater than 90%. For someapplications, each laser diode 36 may have its own collimating lens 130,such as is shown in FIG. 26A. Alternatively, the plurality of laserdiodes 36 may share a collimating lens 130, the collimating lens beingdisposed between beam splitter 162 and pattern generating opticalelement 38, such as is shown in FIG. 26B. Pattern generating opticalelement 38 may be DOE 39, segmented DOE 122, micro-lens array 132, orcompound diffractive periodic structure 136.

As described hereinabove, a sparse distribution 34 improves capture byproviding an improved balance between reducing the amount of projectedlight while maintaining a useful amount of information. For someapplications, in order to provide a higher density pattern withoutreducing capture, a plurality of laser diodes 36 having differentwavelengths may be combined. For example, each structured lightprojector 22 may include at least two, e.g., at least three, laserdiodes 36 that transmit light at distinct respective wavelengths.Although projected spots 33 may be nearly overlapping in some cases, thedifferent color spots may be resolved in space using the camera sensors'color distinguishing capabilities. Optionally, red, blue, and greenlaser diodes may be used. All of the structured light projectorconfigurations described hereinabove may be implemented using aplurality of laser diodes 36 in each structured light projector 22.

Reference is now made to FIGS. 27A-B, which are schematic illustrationsof different ways to combine laser diodes of different wavelengths, inaccordance with some applications of the present invention. Combiningtwo or more lasers of different wavelengths into the same diffractiveelement can be done using a fiber coupler 164 (FIG. 27A) or a lasercombiner 166 (FIG. 27B). For laser combiner 166 the combining elementmay be a dichroic two-way or three-way dichroic combiner. Within eachstructured light projector 22 all laser diodes 36 transmit light througha common pattern generating optical element 38, either simultaneously orat different times. The respective laser beams may hit slightlydifferent positions in pattern generating optical element 38 and createdifferent patterns. These patterns will not interfere with each otherdue to different colors, different times of pulse, or different angles.Using fiber coupler 164 or laser combiner 166 allows for laser diodes 36to be disposed in a remote enclosure 168. Remote enclosure 168 may bedisposed in a proximal end of handheld wand 20, thus allowing for asmaller probe 28.

For some applications, structured light projectors 22 and cameras 24 maybe disposed in proximal end 100 of probe 28.

The following description relates predominantly to applications of thepresent invention that include a light field camera.

Reference is now made to FIG. 28A, which is a schematic illustration ofan intraoral scanner 1020, in accordance with some applications of thepresent invention. Intraoral scanner 1020 comprises an elongate handheldwand 1022 that has a probe 1028 at distal end 1026 of handheld wand1022. Probe 1028 has a distal end 1027 and a proximal end 1024. As usedthroughout the present application, including in the claims, theproximal end of the handheld wand is defined as the end of the handheldwand that is closest to a user's hand when the user is holding thehandheld wand in a ready-for-use position, and the distal end of thehandheld wand is defined as the end of the handheld wand that isfarthest from the user's hand when the user is holding the handheld wandin a ready-for-use position.

For some applications, a single structured light projector 1030 isdisposed in proximal end 1024 of probe 1028, a single light field camera1032 is disposed in proximal end 1024 of probe 1028, and a mirror 1034is disposed in distal end 1027 of probe 1028. Structured light projector1030 and light field camera 1032 are positioned to face mirror 1034, andmirror 1034 is positioned to reflect light from structured lightprojector 1030 directly onto an object 1036 being scanned and reflectlight from object 1036 being scanned into light field camera 1032.

Structured light projector 1030 includes a light source 1040. In someapplications, structured light projector 1030 may have a field ofillumination ψ (psi) of at least 6 degrees and/or less than 30 degrees.In some applications, structured light projector 1030 focuses light fromlight source 1040 at a projector focal plane 1038 (such as is shown inFIGS. 29A-B) that may be located at least 30 mm and/or less than 140 mmfrom light source 1040. Structured light projector 1030 may have apattern generator 1042 that is disposed in the optical path betweenlight source 1040 and projector focal plane 1038. Pattern generator 1042generates a structured light pattern at projector focal plane 1038 whenlight source 1040 is activated to transmit light through patterngenerator 1042.

Light field camera 1032 may have a field of view ω (omega) of at least 6degrees and/or less than 30 degrees. Light field camera 1032 may focusat a camera focal plane 1039 (such as is shown in FIG. 30) that may belocated at least 30 mm and/or less than 140 mm from light field camera1032. Light field camera 1032 has a light field camera sensor 1046 thatcomprises an image sensor 1048 comprising an array of pixels, e.g., aCMOS image sensor, and an array of micro-lenses 1050 disposed in frontof image sensor 1048 such that each micro-lens 1050 is disposed over asub-array 1052 of sensor pixels. Light field camera 1032 additionallyhas an objective lens 1054 disposed in front of light field camerasensor 1048 that forms an image of object 1036 being scanned onto lightfield camera sensor 1046.

Intraoral scanner 1020 may include control circuitry 1056 that (a)drives structured light projector 1030 to project a structured lightpattern onto object 1036 outside handheld wand 1022, and (b) driveslight field camera 1032 to capture a light field that results from thestructured light pattern reflecting off object 1036. The structuredlight field contains information about the intensity of the structuredlight pattern reflecting off object 1036 and the direction of the lightrays. The light field also contains information about phase-encodeddepth via which the scene depth can be estimated from differentdirections. Using information from the captured light field, a computerprocessor 1058 may reconstruct a 3-dimensional image of the surface ofobject 1036, and may output the image to an output device 1060, e.g., amonitor. It is noted that computer processor 1058 is shown in FIGS. 28A,31, and 32, by way of illustration and not limitation, to be outside ofhandheld wand 1022. For other applications, computer processor 1058 maybe disposed within handheld wand 1022.

In some applications, object 1036 being scanned is at least one toothinside a subject's mouth. As described hereinabove, dentists frequentlycoat a subject's teeth with an opaque powder in order to improve imagecapture when using a digital intraoral scanner. Light field camera 1032in intraoral scanner 1020 may capture the light field from thestructured light pattern reflecting off the tooth without the presenceof such a powder on the tooth, enabling a simpler digital intraoralscanning experience.

When structured light projector 1030 and light field camera 1032 aredisposed in proximal end 1024 of probe 1028, the size of probe 1028 islimited by the angle at which mirror 1034 is placed. In someapplications, a height H2 of probe 1028 is less than 17 mm, and a widthW1 of probe 1028 is less than 22 mm, height H2 and width W1 defining aplane that is perpendicular to a longitudinal axis 1067 of handheld wand1022. Furthermore, height H2 of probe 1028 is measured from a lowersurface 1070 (scanning surface), through which reflected light fromobject 1036 being scanned enters probe 1028, to an upper surface 1072opposite lower surface 1070. In some applications, height H2 is between14-17 mm. In some applications, width W1 is between 18-22 mm.

Reference is now made to FIG. 29A, which is a schematic illustration ofstructured light projector 1030 having a laser diode 1041 as lightsource 1040, in accordance with some applications of the presentinvention. For some applications, pattern generator 1042 may be adiffractive optical element (DOE) 1043. Laser diode 1041 may transmitlight through a collimator 1062, and the collimated light is thentransmitted through DOE 1043 in order to generate the structured lightpattern as a distribution of discrete unconnected spots of light.Alternatively to DOE 1043, pattern generator 1042 may be a refractivemicro-lens array disposed in the optical path between laser diode 1041and the projector focal plane (configuration not shown).

Reference is now made to FIG. 29B, which is a schematic illustration ofstructured light projector 1030 having a light emitting diode (LED) 1064as light source 1040, and a mask 1066 as pattern generator 1042.

Reference is now made to FIG. 30, which is a schematic illustration oflight field camera 1032, showing light field camera sensor 1046, and athree-dimensional object 1036 being captured, in accordance with someapplications of the present invention. For some applications, opticalparameters of light field camera 1032 may be chosen such that (a) lightreflected off a foreground 1075 of object 1036 is focused onto a centralregion 1074 of light field camera sensor, and (b) light reflected off abackground 1077 of object 1036 is focused onto a peripheral region 1076of light field camera sensor 1046. In some applications, when scanningan intraoral scene, peripheral region 1076 may be directed towardfarther objects, such as gingiva, more frequently than nearer objects,such as teeth.

Central region 1074 of light field camera sensor 1046 may have a higherspatial resolution than peripheral region 1076 of light field camerasensor 1046. For example, each one of sub-arrays 1052 in central region1074 of image sensor 1048 may have 10-40% fewer pixels than each one ofsub-arrays 1052 in peripheral region 1076, i.e., the micro-lenses incentral region 1074 may be smaller than the micro-lenses in peripheralregion 1076. Smaller micro-lenses allow for more micro-lenses per unitarea in central region 1074. Thus, central region 1074 of light fieldcamera sensor 1046 may have a higher spatial resolution due to theincreased ratio of micro-lenses per unit area. In some applications,central region 1074 may include at least 50% of the total number ofsensor pixels.

While central region 1074 has higher spatial resolution than peripheralregion 1076, peripheral region 1076 may have a higher depth resolutionthan central region 1074, and may be set to focus at farther objectdistances than in central region 1074. The larger micro-lenses inperipheral region 1076 of light field camera sensor 1046 are configuredto focus at a higher depth than the smaller micro-lenses in centralregion 1074. For example, each micro-lens 1050 disposed over a sub-array1052 of sensor pixels in peripheral region 1076 of the image sensor 1048may be configured to focus at a depth that is 1.1-1.4 times larger thana depth at which each micro-lens 1050 disposed over a sub-array 1052 ofsensor pixels in central region 1074 of image sensor 1048 is configuredto focus.

Thus, the higher spatial resolution of central region 1074 may allowforeground 1075 of object 1036 to be captured at a higher spatialresolution than background 1077 of object 1036, e.g., when scanning anintraoral scene of a subject, the teeth may be captured at a higherspatial resolution than areas surrounding the teeth, while the fartherfocus and higher depth resolution of peripheral region 1076 may allowfor the capture of background 1077, e.g., edentulous regions and gingivasurrounding the teeth in foreground 1075.

Reference is now made to FIG. 31, which is a schematic illustration ofintraoral scanner 1020 with structured light projector 1030 and lightfield camera 1032 disposed in distal end 1027 of probe 1028, inaccordance with some applications of the present invention. For someapplications, exactly one structured light projector 1030 and exactlyone light field camera 1032 are disposed in distal end 1027 of probe1028. Structured light projector 1030 may be positioned to directly facean object 1036 outside handheld wand 1022 placed in its field ofillumination. Thus, light projected from structured light projector 1030will fall on object 1036 without any optical redirection, e.g.,reflection off a mirror in order to redirect the light such as describedhereinabove with reference to FIG. 28A. Similarly, light field camera1032 may be positioned to directly face object 1036 outside handheldwand 1022 placed in its field of view. Thus, light reflecting off object1036 will enter light field camera 1032 without any optical redirection,e.g., reflection off a mirror in order to redirect the light such asdescribed hereinabove with reference to FIG. 28A.

Positioning structured light projector 1030 in distal end 1027 of probe1028 may allow field of illumination ψ (psi) of structured lightprojector 1030 to be wider, e.g., at least 60 degrees and/or less than120 degrees. Positioning structured light projector 1030 in distal end1027 of probe 1028 may also allow structured light projector 1030 tofocus light from light source 1040 at a projector focal plane that maybe located at least 3 mm and/or less than 40 mm from light source 1040.

Positioning light field camera 1032 in distal end 1027 of probe 1028 mayallow field of view ω (omega) of light field camera 1032 to be wider,e.g., at least 60 degrees and/or less than 120 degrees. Positioninglight field camera 1032 in distal end 1027 of probe 1028 may also allowlight field camera 1032 to focus at a camera focal plane that may belocated at least 3 mm and/or less than 40 mm from light source 1040. Insome applications, field of illumination ψ (psi) of structured lightprojector 1030 and field of view ω (omega) of light field camera 1032overlap such that at least 40% of the projected structured light patternfrom structured light projector 1030 is in field of view ω (omega) oflight field camera 1032. Similarly to as described hereinabove withreference to FIG. 30, when intraoral scanner 1020 has a single lightfield camera 1032 disposed in distal end 1027 of probe 1028, opticalparameters of light field camera sensor 1046 may be chosen such that acentral region of light field camera sensor 1090 has a higher resolutionthan a peripheral region of light field camera sensor 1046.

Positioning structured light projector 1030 and light field camera 1032in distal end 1027 of probe 1028 may enable probe 1028 to be smallersince mirror 1034 is not used in this configuration. In someapplications, height H3 of probe 1028 is less than 14 mm, and width W2of probe 1028 is less than 22 mm, height H3 and width W2 defining aplane that is perpendicular to a longitudinal axis 1067 of handheld wand1022. In some applications, height H3 is between 10-14 mm. In someapplications, width W2 is between 18-22 mm. As described hereinabove,height H3 of probe 1028 is measured from (a) a lower surface 1070(scanning surface), through which reflected light from object 1036 beingscanned enters probe 1028, to (b) an upper surface 1072 opposite lowersurface 1070. Control circuitry 1056 (a) may drive structured lightprojector 1030 to project a structured light pattern onto object 1036outside handheld wand 1022, and (b) may drive light field camera 1032 tocapture a light field resulting from the structured light patternreflecting off object 1036. Using information from the captured lightfield, computer processor 1058 may reconstruct a 3-dimensional image ofthe surface of objects 1036, and output the image to an output device1060, e.g., a monitor.

Reference is now made to FIG. 32, which is a schematic illustration ofintraoral scanner 1020 with a plurality of structured light projectors1030 and a plurality of light field cameras 1032 disposed in distal end1027 of probe 1028, in accordance with some applications of the presentinvention. Having a plurality of structured light projectors and aplurality of light field cameras may increase a general field of view ofintraoral scanner 1020, which may enable capturing a plurality ofobjects 1036, e.g., capturing a plurality of teeth as well as regionsaround the teeth, e.g., edentulous regions in a subject's mouth. In someapplications, a plurality of fields of illumination ψ (psi) overlap witha respective plurality of fields of view ω (omega), such that at least40% of the projected structured light pattern from each structured lightprojector 1030 is in a field of view ω (omega) of at least one lightfield camera 1032. Control circuitry 1056 (a) may drive the plurality ofstructured light projectors 1030 to each project a structured lightpattern onto object 1036 outside handheld wand 1022, and (b) may drivethe plurality of light field cameras 1032 to capture a light fieldresulting from the plurality of structured light patterns reflecting offobject 1036. Using information from the captured light field, computerprocessor 1058 may reconstruct a 3-dimensional image of the surface ofobjects 1036, and output the image to an output device 1060, e.g., amonitor.

For some applications, at least one of structured light projectors 1030may be a monochrome structured light projector that projects amonochrome structured light pattern onto object 1036 being scanned. Forexample, the monochrome structured light projector may project a bluestructured light pattern at a wavelength of 420-470 nm. At least one oflight field cameras 1032 may be a monochrome light field camera thatcaptures a light field resulting from the monochrome structured lightpattern reflecting off object 1036 being scanned. Intraoral scanner 1020may further include a light source that transmits white light ontoobject 1036 and a camera that captures a 2-dimensional color image ofobject 1036 under the white light illumination. Computer processor 1058may combine (a) information captured from the monochrome light fieldwith (b) at least one 2-dimensional color image of object 1036 in orderto reconstruct a 3-dimensional image of the surface of objects 1036.Computer processor 1058 may then output the image to an output device1060, e.g., a monitor.

Any of the aforementioned apparatuses may be used to perform methods ofgenerating image data (e.g., of an intraoral surface. In one exampleimplementation, a method includes generating, by one or more lightprojectors disposed in a probe of an intraoral scanner, respective lightpatterns. Generating a light pattern by a light projector of the one ormore light projectors may include generating light by a light projector,focusing the light at a projector focal plane, and generating, by apattern generator, a light pattern from the light at the projector focalplane. The method may further include projecting the respective lightpatterns of the one or more light projectors toward an intraoral surfacedisposed in a field of illumination of the one or more light projectors.The method may further include receiving, by one or more light fieldcameras disposed in the probe, a light field resulting from at least aportion of the respective light patterns reflecting off of the intraoralsurface. The method may further include generating a plurality of imagesby the one or more light field cameras that depict the light field, andsending the plurality of images to a data processing system.

In some implementations, the one or more light projectors and the one ormore light field cameras are disposed in a distal end of the probe, andthe one or more light projectors and the one or more light field camerasare positioned such that (a) each light projector directly faces theintraoral surface, (b) each light field camera directly faces theintraoral surface, and (c) at least 40% of the light pattern from eachlight projector is in a field of view of at least one of the light fieldcameras.

In some implementations, the one or more light projectors and the lightfield camera are disposed in a proximal end of the probe. For suchimplementations the method may further include using a mirror to reflectthe respective light patterns onto the intraoral surface, and using themirror to reflect the light field reflected from the intraoral surfaceinto the one or more light field cameras.

In some applications of the invention, a method may be performed by anyof the described apparatuses for intraoral scanning (e.g., intraoralscanners and/or data processing systems such as computer processor 1058)to generate a digital three-dimensional model of an intraoral surface.In one embodiment, the method includes driving one or more lightprojectors of an intraoral scanner to project a light pattern on theintraoral surface. The method further includes driving one or more lightfield cameras of the intraoral scanner to capture a plurality of imagesthat depict a light field resulting from at least a portion of theprojected light pattern reflecting off of the intraoral surface, whereinthe light field contains information about an intensity of the lightpattern reflecting off of the intraoral surface and a direction of lightrays. The method further includes receiving the plurality of images thatdepict at least a portion of a projected light pattern on the intraoralsurface and using information from the captured light field depicted inthe plurality of images to generate the digital three-dimensional modelof the intraoral surface.

In one application, at least 40% of the light pattern from each lightprojector is in a field of view of at least one of the one or more lightfield cameras. In one application, each light projector is a structuredlight projector that has a field of illumination of 60-120 degrees, andwherein the projector focal plane is located between 3 mm and 40 mm fromthe light source. In one application, each light field camera has afield of view of 60-120 degrees and is configured to focus at a camerafocal plane that is located between 3 mm and 40 mm from the light fieldcamera. In one application, the plurality of images comprise images froma plurality of light field cameras. In one application, the light fieldfurther contains information about phase-encoded depth via which depthcan be estimated from different directions. In one application, themethod further includes receiving a plurality of two-dimensional colorimages of the intraoral surface, and determining color data for thedigital three-dimensional model of the intraoral surface based on theplurality of two-dimensional color images.

Applications of the invention described herein can take the form of acomputer program product accessible from a computer-usable orcomputer-readable medium (e.g., a non-transitory computer-readablemedium) providing program code for use by or in connection with acomputer or any instruction execution system, such as processor 96 orprocessor 1058. For the purpose of this description, a computer-usableor computer readable medium can be any apparatus that can comprise,store, communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. In some applications, the computer-usable orcomputer readable medium is a non-transitory computer-usable or computerreadable medium.

Examples of a computer-readable medium include a semiconductor orsolid-state memory, magnetic tape, a removable computer diskette, arandom-access memory (RAM), a read-only memory (ROM), a rigid magneticdisk and an optical disk. Current examples of optical disks includecompact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W)and DVD. For some applications, cloud storage, and/or storage in aremote server is used.

A data processing system suitable for storing and/or executing programcode will include at least one processor (e.g., processor 96, orprocessor 1058) coupled directly or indirectly to memory elementsthrough a system bus. The memory elements can include local memoryemployed during actual execution of the program code, bulk storage, andcache memories which provide temporary storage of at least some programcode in order to reduce the number of times code must be retrieved frombulk storage during execution. The system can read the inventiveinstructions on the program storage devices and follow theseinstructions to execute the methodology of the applications of theinvention.

Network adapters may be coupled to the processor to enable the processorto become coupled to other processors or remote printers or storagedevices through intervening private or public networks. Modems, cablemodem and Ethernet cards are just a few of the currently available typesof network adapters.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object-oriented programming language such asJava, Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the C programming language or similar programminglanguages.

It will be understood that the methods described herein can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general-purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer (e.g., processor 96 orprocessor 1058) or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the methodsdescribed in the present application. These computer programinstructions may also be stored in a computer-readable medium (e.g., anon-transitory computer-readable medium) that can direct a computer orother programmable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instruction meanswhich implement the function/act specified in the methods described inthe present application. The computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed on the computeror other programmable apparatus to produce a computer implementedprocess such that the instructions which execute on the computer orother programmable apparatus provide processes for implementing thefunctions/acts specified in the methods described in the presentapplication.

Processor 96 and processor 1058 are typically hardware devicesprogrammed with computer program instructions to produce respectivespecial purpose computers. For example, when programmed to perform themethods described herein, the computer processor typically acts as aspecial purpose 3-D surface reconstruction computer processor.Typically, the operations described herein that are performed bycomputer processors transform the physical state of a memory, which is areal physical article, to have a different magnetic polarity, electricalcharge, or the like depending on the technology of the memory that isused.

Alternatively, processor 96 may take the form of a field programmablegate array (FPGA), an application-specific integrated circuit (ASIC), ora neural network implemented on a specialized chip.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. An apparatus for intraoral scanning, the apparatus comprising: anelongate handheld wand comprising a probe at a distal end of theelongate handheld wand; one or more light projectors, each lightprojector comprising at least one light source and a pattern generatingoptical element, wherein each light projector is configured to project apattern of light defined by a plurality of projector rays when the lightsource is activated; two or more cameras, each of the two or morecameras comprising a camera sensor having an array of pixels, whereineach of the two or more cameras is configured to capture a plurality ofimages that depict at least a portion of the projected pattern of lighton an intraoral surface; and one or more processors configured to:access calibration data that associates camera rays corresponding topixels on the camera sensor of each of the two or more cameras toprojector rays of the plurality of projector rays; determineintersections of projector rays and camera rays corresponding to atleast the portion of the projected pattern of light using thecalibration data, wherein intersections of the projector rays and thecamera rays are associated with three-dimensional points in space;identify three-dimensional locations of the projected pattern of lightbased on agreements of the two or more cameras on there being theprojected pattern of light by projector rays at certain intersections;and use the identified three-dimensional locations to generate a digitalthree-dimensional model of the intraoral surface.
 2. The apparatus ofclaim 1, wherein the pattern of light comprises a plurality of spots,and wherein each of the plurality of projector rays corresponds to aspot of the plurality of spots.
 3. The apparatus of claim 2, whereineach projector ray corresponds to a respective path of pixels on thecamera sensor of a respective one of the two or more cameras, andwherein to identify the three-dimensional locations the one or moreprocessors run a correspondence algorithm to: for each projector ray i,identify for each detected spot j on a camera sensor path correspondingto projector ray i, how many other cameras, on their respective camerasensor paths corresponding to projector ray i, detected respective spotsk corresponding to respective camera rays that intersect projector ray iand a camera ray corresponding to detected spot j, wherein projector rayi is identified as a specific projector ray that produced a detectedspot j for which the highest number of other cameras detected respectivespots k; and compute a respective three-dimensional position on theintraoral surface at an intersection of projector ray i and therespective camera rays corresponding to the detected spot j and therespective detected spots k.
 4. The apparatus of claim 3, wherein toidentify the three-dimensional locations, the one or more processors arefurther to: remove from consideration projector ray i, and therespective camera rays corresponding to the detected spot j and therespective detected spots k; and run the correspondence algorithm againfor a next projector ray i.
 5. The apparatus of claim 3, furthercomprising: a temperature sensor; wherein the one or more processors arefurther configured to: receive temperature data from the temperaturesensor, wherein the temperature data is indicative of a temperature ofat least one of the one or more light projectors or the two or morecameras; and based on the temperature data, select between a pluralityof sets of stored calibration data corresponding to a plurality ofrespective temperatures, each set of stored calibration data indicatingfor a respective temperature (a) the projector ray corresponding to eachof the projected spots of light from each one of the one or moreprojectors, and (b) the camera ray corresponding to each pixel on thecamera sensor of each one of the one or more cameras.
 6. The apparatusof claim 2, wherein the pattern of light comprises a non-codedstructured light pattern, and wherein the plurality of spots comprisesan approximately uniform distribution of discrete unconnected spots oflight.
 7. The apparatus of claim 2, wherein the plurality of spotscomprises a first subset of spots having a first wavelength and a secondsubset of spots having a second wavelength, and wherein the calibrationdata comprises first calibration data for the first wavelength andsecond calibration data for the second wavelength.
 8. The apparatus ofclaim 1, further comprising: a target having a plurality of regions;wherein: each light projector has at least one region of the target inits field of illumination; each camera has at least one region of thetarget in its field of view; a plurality of the regions of the targetare in the field of view of one of the cameras and in the field ofillumination of one of the light projectors; and the one or moreprocessors are further configured to: receive data from the two or morecameras indicative of a position of the target with respect to thepattern of light; compare the received data to a stored calibrationposition of the target, wherein a discrepancy between (i) the receiveddata indicative of the position of the target and (ii) the storedcalibration position of the target indicates a shift of the projectorrays and the camera rays from their respective calibration values; andaccount for the shift of the projector rays and the camera rays inidentification of the three-dimensional locations.
 9. The apparatus ofclaim 1, wherein the one or more processors are further configured to:drive each one of the one or more light projectors to project thepattern of light on the intraoral surface; and drive each one of the twoor more cameras to capture the plurality of images.
 10. The apparatus ofclaim 1, wherein the one or more light projectors comprise a pluralityof structured light projectors, wherein each of plurality of structuredlight projectors is to project respective distributions of discreteunconnected spots of light on the intraoral surface simultaneously or atdifferent times.
 11. The apparatus of claim 1, wherein the patterngenerating optical element comprises a diffractive optical element or arefractive optical element.
 12. The apparatus of claim 1, wherein thetwo or more cameras are configured to focus at an object focal planethat is located between about 1 mm and about 30 mm from a camera lensthat is farthest from the camera sensor.
 13. An apparatus for intraoralscanning, the apparatus comprising: an elongate handheld wand comprisinga probe at a distal end of the elongate handheld wand; one or more lightprojectors, each light projector comprising: at least one light sourceconfigured to generate light when activated; and a pattern generatingoptical element, wherein the pattern generating optical element isconfigured to generate a pattern of light when the light is transmittedthrough the pattern generating optical element; and two or more cameras,each of the two or more cameras comprising a camera sensor and one ormore lenses, wherein each of the two or more cameras is configured tocapture a plurality of images that depict at least a portion of theprojected pattern of light on an intraoral surface, wherein each camerais configured to focus at an object focal plane that is located betweenabout 1 mm and about 30 mm from a lens of the one or more lenses that isfarthest from the camera sensor.
 14. The apparatus of claim 13, whereinthe one or more light projectors are disposed within the probe, andwherein the two or more cameras are disposed within the probe.
 15. Theapparatus of claim 14, wherein: the one or more light projectorscomprise at least two light projectors and the two or more camerascomprise at least four cameras; a majority of the at least two lightprojectors and the at least four cameras are arranged in at least tworows that are each approximately parallel to a longitudinal axis of theprobe, the at least two rows comprising at least a first row and asecond row; a distal-most camera along the longitudinal axis and aproximal-most camera along the longitudinal axis of the at least fourcameras are positioned such that their optical axes are at an angle of90 degrees or less with respect to each other from a line of sight thatis perpendicular to the longitudinal axis; and cameras in the first rowand cameras in the second row are positioned such that optical axes ofthe cameras in the first row are at an angle of 90 degrees or less withrespect to optical axes of the cameras in the second row from a line ofsight that is coaxial with the longitudinal axis of the probe.
 16. Theapparatus of claim 15, wherein: a remainder of the at least four camerasother than the distal-most camera and the proximal-most camera haveoptical axes that are substantially parallel to the longitudinal axis ofthe probe; and each of the at least two rows comprises an alternatingsequence of light projectors and cameras.
 17. The apparatus of claim 16,wherein the at least four cameras comprise at least five cameras,wherein the at least two light projectors comprise at least five lightprojectors, wherein a proximal-most component in the first row is alight projector, and wherein a proximal-most component in the second rowis a camera.
 18. The apparatus of claim 15, wherein: the distal-mostcamera along the longitudinal axis and the proximal-most camera alongthe longitudinal axis are positioned such that their optical axes are atan angle of 35 degrees or less with respect to each other from the lineof sight that is perpendicular to the longitudinal axis; and the camerasin the first row and the cameras in the second row are positioned suchthat the optical axes of the cameras in the first row are at an angle of35 degrees or less with respect to the optical axes of the cameras inthe second row from the line of sight that is coaxial with thelongitudinal axis of the probe.
 19. The apparatus of claim 13, whereinthe pattern of light is defined by a plurality of projector rays, theapparatus further comprising one or more processors configured to:access calibration data that associates camera rays corresponding topixels on the camera sensor of each of the two or more cameras toprojector rays of the plurality of projector rays; determineintersections of projector rays and camera rays corresponding to theportion of the projected pattern of light using the calibration data,wherein intersections of the camera rays and the projector rays areassociated with three-dimensional points in space; identifythree-dimensional locations of the projected pattern of light based onagreements of the two or more cameras on there being the projectedpattern of light by projector rays at certain intersections; and use theidentified three-dimensional locations to generate a digitalthree-dimensional model of the intraoral surface.
 20. The apparatus ofclaim 13, wherein the one or more structured light projectors are eachconfigured to generate a distribution of discrete unconnected spots oflight at all planes located between 1 mm and 30 mm from the patterngenerating optical element.
 21. The apparatus of claim 13, wherein eachof the one or more structured light projectors has a field ofillumination of about 45 degrees to about 120 degrees, and wherein eachof the two or more cameras has a field of view of about 45 degrees toabout 120 degrees.
 22. The apparatus of claim 13, wherein the patterngenerating optical element is configured to utilize at least one ofdiffraction or refraction to generate the pattern of light, and whereinthe pattern generating optical element has a light throughput efficiencyof at least 90%.
 23. The apparatus of claim 13, further comprising: atleast one uniform light projector configured to project white light ontothe intraoral surface, wherein at least one of the two or more camerasis configured to capture two-dimensional color images of the intraoralsurface using illumination from the uniform light projector.
 24. Theapparatus of claim 13, wherein the pattern generating optical elementcomprises a diffractive optical element (DOE).
 25. The apparatus ofclaim 24, wherein the DOE is segmented into a plurality of sub-DOEpatches arranged in an array, wherein each sub-DOE patch generates arespective distribution of discrete unconnected spots of light in adifferent area of a field of illumination such that the distribution ofdiscrete unconnected spots of light is generated when the light sourceis activated.
 26. The apparatus according to claim 13, wherein each ofthe one or more projectors comprises an additional optical elementdisposed between the light source and the pattern generating opticalelement, the additional optical element being configured to generate aBessel beam from the light that is transmitted through the additionaloptical element, wherein the pattern of light comprises a pattern ofdiscrete unconnected spots of light that maintain a diameter of lessthan 0.06 mm through every inner surface of a geometric sphere that iscentered at the pattern generating optical element and that has a radiusof between 1 mm and 30 mm.
 27. The apparatus of claim 26, wherein theadditional optical element comprises an axicon lens.
 28. The apparatusof claim 13, wherein the light pattern comprises a distribution ofdiscrete unconnected spots of light, wherein a ratio of illuminated areato non-illuminated area for each orthogonal plane in a field ofillumination is 1:150-1:16.
 29. An apparatus for intraoral scanning, theapparatus comprising: an elongate handheld wand comprising a probe at adistal end of the elongate handheld wand; one or more light projectorsdisposed within the probe, each light projector comprising: a lightsource configured to generate light when activated; a first opticalelement configured to generate a Bessel beam from the light that istransmitted through the first optical element; a pattern generatingoptical element, wherein the pattern generating optical element isconfigured to generate a pattern of light when the Bessel beam istransmitted through the pattern generating optical element; and two morecameras, each camera comprising a camera sensor and objective opticscomprising one or more lenses, wherein each camera is configured tocapture a plurality of images that depict at least a portion of theprojected pattern of light on an intraoral surface.
 30. The apparatus ofclaim 29, wherein the pattern of light comprises a pattern of discreteunconnected spots of light that maintain a substantially uniform size atany orthogonal plane located between about 1 mm and about 30 mm from thepattern generating optical element.
 31. The apparatus of claim 30,wherein the spots have a diameter of less than 0.06 mm through everyinner surface of a geometric sphere that is centered at the patterngenerating optical element and that has a radius of between 1 mm and 30mm.
 32. The apparatus of claim 29, wherein the first optical elementcomprises an axicon lens.
 33. The apparatus of claim 32, wherein theaxicon lens has an axicon head angle of 0.2-2 degrees.
 34. The apparatusof claim 29, further comprising a beam shaping optical element betweenthe first optical element and the light source, wherein the beam shapingoptical element comprises a collimating lens.
 35. The apparatus of claim29, wherein each camera is configured to focus at an object focal planethat is located between about 1 mm and about 30 mm from a lens of theone or more lenses that is farthest from the camera sensor.
 36. Theapparatus of claim 29, wherein each of the one or more structured lightprojectors has a field of illumination of about 45 degrees to about 120degrees, wherein each of the two or more cameras has a field of view ofabout 45 degrees to about 120 degrees, and wherein the light sourcecomprises at least one laser diode.
 37. A method of generating a digitalthree-dimensional model of an intraoral surface, comprising: receiving aplurality of images that depict at least a portion of a projectedpattern of light on an intraoral surface, the projected pattern of lighthaving been projected by one or more light projectors of an intraoralscanner, the pattern of light being defined by a plurality of projectorrays, and the plurality of images having been generated by two or morecameras of the intraoral scanner; accessing calibration data thatassociates camera rays corresponding to pixels on a camera sensor ofeach of the two or more cameras to projector rays of the plurality ofprojector rays; determining intersections of projector rays and camerarays corresponding to at least the portion of the projected pattern oflight using the calibration data, wherein intersections of the projectorrays and the camera rays are associated with three-dimensional points inspace; identifying three-dimensional locations of the projected patternof light based on agreements of the two or more cameras on there beingthe projected pattern of light by projector rays at certainintersections; and using the identified three-dimensional locations togenerate the digital three-dimensional model of the intraoral surface.38. The method of claim 37, wherein the pattern of light comprises aplurality of spots, and wherein each of the plurality of projector rayscorresponds to a spot of the plurality of spots.
 39. The method of claim38, wherein each projector ray corresponds to a respective path ofpixels on the camera sensor of a respective one of the two or morecameras, and wherein identifying the three-dimensional locationscomprises running a correspondence algorithm to: for each projector rayi, identify for each detected spot j on a camera sensor pathcorresponding to projector ray i, how many other cameras, on theirrespective camera sensor paths corresponding to projector ray i,detected respective spots k corresponding to respective camera rays thatintersect projector ray i and a camera ray corresponding to detectedspot j, wherein projector ray i is identified as a specific projectorray that produced a detected spot j for which the highest number ofother cameras detected respective spots k; and compute a respectivethree-dimensional position on the intraoral surface at an intersectionof projector ray i and the respective camera rays corresponding to thedetected spot j and the respective detected spots k.
 40. The method ofclaim 39, wherein identifying the three-dimensional locations furthercomprises: removing from consideration projector ray i, and therespective camera rays corresponding to the detected spot j and therespective detected spots k; and running the correspondence algorithmagain for a next projector ray i.
 41. The method of claim 38, furthercomprising: receiving temperature data generated by a temperature sensorof the intraoral scanner, wherein the temperature data is indicative ofa temperature of at least one of the one or more light projectors or thetwo or more cameras; and based on the temperature data, selectingbetween a plurality of sets of stored calibration data corresponding toa plurality of respective temperatures, each set of stored calibrationdata indicating for a respective temperature (a) the projector raycorresponding to each of the projected spots of light from each one ofthe one or more projectors, and (b) the camera ray corresponding to eachpixel on camera sensors of each one of the two or more cameras.
 42. Themethod of claim 38, wherein the pattern of light comprises a non-codedstructured light pattern, and wherein the plurality of spots comprisesan approximately uniform distribution of discrete unconnected spots oflight.
 43. The method of claim 38, wherein the plurality of spotscomprises a first subset of spots having a first wavelength and a secondsubset of spots having a second wavelength, and wherein the calibrationdata comprises first calibration data for the first wavelength andsecond calibration data for the second wavelength.
 44. The method ofclaim 37, further comprising: receiving data from the two or morecameras indicative of a position of a target of the intraoral scannerwith respect to the pattern of light, wherein the target has a pluralityof regions, each light projector has at least one region of the targetin its field of illumination, and each camera has at least one region ofthe target in its field of view; comparing the received data to a storedcalibration position of the target, wherein a discrepancy between (i)the received data indicative of the position of the target and (ii) thestored calibration position of the target indicates a shift of theprojector rays and the camera rays from their respective calibrationvalues; and accounting for the shift of the projector rays and thecamera rays in identification of the three-dimensional locations. 45.The method of claim 37, further comprising: driving each one the of theone or more light projectors to project the pattern of light on theintraoral surface; and driving each one of the two or more cameras tocapture the plurality of images.